[X86] Treat __ehdr_start as large (#79884)

aeubanks · web-flow · commit d6e07e084511 · 2024-01-29T14:25:40.000-08:00
The __ehdr_start symbol is added by the linker and points to the ELF file headers, which can be very far away from text. Treat it as a large symbol under the medium/large code models. Performance to access __ehdr_start is almost certainly not important. There are a couple of other symbols that the linker adds [1], but this is the most relevant one that may be far away from text. [1] https://github.com/llvm/llvm-project/blob/547c395b279a93357082ac06cf3e8fe37ebfc3fe/lld/ELF/Writer.cpp#L226
diff --git a/llvm/lib/Target/TargetMachine.cpp b/llvm/lib/Target/TargetMachine.cpp
@@ -85,6 +85,8 @@ bool TargetMachine::isLargeGlobalValue(const GlobalValue *GVal) const {
       getCodeModel() == CodeModel::Large) {
     if (!GV->getValueType()->isSized())
       return true;
+    if (GV->isDeclaration() && GV->getName() == "__ehdr_start")
+      return true;
     const DataLayout &DL = GV->getParent()->getDataLayout();
     uint64_t Size = DL.getTypeSizeInBits(GV->getValueType()) / 8;
     return Size == 0 || Size > LargeDataThreshold;
diff --git a/llvm/test/CodeGen/X86/code-model-elf.ll b/llvm/test/CodeGen/X86/code-model-elf.ll
@@ -57,6 +57,7 @@ target triple = "x86_64--linux"
 @opaque = external dso_local global %t
 @forced_small_data = dso_local global [10 x i32] zeroinitializer, code_model "small", align 16
 @forced_large_data = dso_local global [10 x i32] zeroinitializer, code_model "large", align 16
+@__ehdr_start = external dso_local global i8
 
 define dso_local ptr @lea_static_data() #0 {
 ; SMALL-STATIC-LABEL: lea_static_data:
@@ -800,6 +801,63 @@ define dso_local ptr @lea_opaque() #0 {
   ret ptr @opaque
 }
 
+define dso_local ptr @lea_ehdr_start() #0 {
+; SMALL-STATIC-LABEL: lea_ehdr_start:
+; SMALL-STATIC:       # %bb.0:
+; SMALL-STATIC-NEXT:    movl $__ehdr_start, %eax
+; SMALL-STATIC-NEXT:    retq
+;
+; MEDIUM-STATIC-LABEL: lea_ehdr_start:
+; MEDIUM-STATIC:       # %bb.0:
+; MEDIUM-STATIC-NEXT:    movabsq $__ehdr_start, %rax
+; MEDIUM-STATIC-NEXT:    retq
+;
+; LARGE-STATIC-LABEL: lea_ehdr_start:
+; LARGE-STATIC:       # %bb.0:
+; LARGE-STATIC-NEXT:    movabsq $__ehdr_start, %rax
+; LARGE-STATIC-NEXT:    retq
+;
+; SMALL-PIC-LABEL: lea_ehdr_start:
+; SMALL-PIC:       # %bb.0:
+; SMALL-PIC-NEXT:    leaq __ehdr_start(%rip), %rax
+; SMALL-PIC-NEXT:    retq
+;
+; MEDIUM-SMALL-DATA-PIC-LABEL: lea_ehdr_start:
+; MEDIUM-SMALL-DATA-PIC:       # %bb.0:
+; MEDIUM-SMALL-DATA-PIC-NEXT:    leaq _GLOBAL_OFFSET_TABLE_(%rip), %rcx
+; MEDIUM-SMALL-DATA-PIC-NEXT:    movabsq $__ehdr_start@GOTOFF, %rax
+; MEDIUM-SMALL-DATA-PIC-NEXT:    addq %rcx, %rax
+; MEDIUM-SMALL-DATA-PIC-NEXT:    retq
+;
+; MEDIUM-PIC-LABEL: lea_ehdr_start:
+; MEDIUM-PIC:       # %bb.0:
+; MEDIUM-PIC-NEXT:    leaq _GLOBAL_OFFSET_TABLE_(%rip), %rcx
+; MEDIUM-PIC-NEXT:    movabsq $__ehdr_start@GOTOFF, %rax
+; MEDIUM-PIC-NEXT:    addq %rcx, %rax
+; MEDIUM-PIC-NEXT:    retq
+;
+; LARGE-PIC-LABEL: lea_ehdr_start:
+; LARGE-PIC:       # %bb.0:
+; LARGE-PIC-NEXT:  .L13$pb:
+; LARGE-PIC-NEXT:    leaq .L13$pb(%rip), %rax
+; LARGE-PIC-NEXT:    movabsq $_GLOBAL_OFFSET_TABLE_-.L13$pb, %rcx
+; LARGE-PIC-NEXT:    addq %rax, %rcx
+; LARGE-PIC-NEXT:    movabsq $__ehdr_start@GOTOFF, %rax
+; LARGE-PIC-NEXT:    addq %rcx, %rax
+; LARGE-PIC-NEXT:    retq
+;
+; LARGE-SMALL-DATA-PIC-LABEL: lea_ehdr_start:
+; LARGE-SMALL-DATA-PIC:       # %bb.0:
+; LARGE-SMALL-DATA-PIC-NEXT:  .L13$pb:
+; LARGE-SMALL-DATA-PIC-NEXT:    leaq .L13$pb(%rip), %rax
+; LARGE-SMALL-DATA-PIC-NEXT:    movabsq $_GLOBAL_OFFSET_TABLE_-.L13$pb, %rcx
+; LARGE-SMALL-DATA-PIC-NEXT:    addq %rax, %rcx
+; LARGE-SMALL-DATA-PIC-NEXT:    movabsq $__ehdr_start@GOTOFF, %rax
+; LARGE-SMALL-DATA-PIC-NEXT:    addq %rcx, %rax
+; LARGE-SMALL-DATA-PIC-NEXT:    retq
+  ret ptr @__ehdr_start
+}
+
 define dso_local void @global_fn() #0 {
 ; CHECK-LABEL: global_fn:
 ; CHECK:       # %bb.0:
@@ -861,19 +919,19 @@ define dso_local ptr @lea_static_fn() #0 {
 ;
 ; LARGE-PIC-LABEL: lea_static_fn:
 ; LARGE-PIC:       # %bb.0:
-; LARGE-PIC-NEXT:  .L16$pb:
-; LARGE-PIC-NEXT:    leaq .L16$pb(%rip), %rax
-; LARGE-PIC-NEXT:    movabsq $_GLOBAL_OFFSET_TABLE_-.L16$pb, %rcx
+; LARGE-PIC-NEXT:  .L17$pb:
+; LARGE-PIC-NEXT:    leaq .L17$pb(%rip), %rax
+; LARGE-PIC-NEXT:    movabsq $_GLOBAL_OFFSET_TABLE_-.L17$pb, %rcx
 ; LARGE-PIC-NEXT:    addq %rax, %rcx
 ; LARGE-PIC-NEXT:    movabsq $static_fn@GOTOFF, %rax
 ; LARGE-PIC-NEXT:    addq %rcx, %rax
 ; LARGE-PIC-NEXT:    retq
 ;
 ; LARGE-SMALL-DATA-PIC-LABEL: lea_static_fn:
 ; LARGE-SMALL-DATA-PIC:       # %bb.0:
-; LARGE-SMALL-DATA-PIC-NEXT:  .L16$pb:
-; LARGE-SMALL-DATA-PIC-NEXT:    leaq .L16$pb(%rip), %rax
-; LARGE-SMALL-DATA-PIC-NEXT:    movabsq $_GLOBAL_OFFSET_TABLE_-.L16$pb, %rcx
+; LARGE-SMALL-DATA-PIC-NEXT:  .L17$pb:
+; LARGE-SMALL-DATA-PIC-NEXT:    leaq .L17$pb(%rip), %rax
+; LARGE-SMALL-DATA-PIC-NEXT:    movabsq $_GLOBAL_OFFSET_TABLE_-.L17$pb, %rcx
 ; LARGE-SMALL-DATA-PIC-NEXT:    addq %rax, %rcx
 ; LARGE-SMALL-DATA-PIC-NEXT:    movabsq $static_fn@GOTOFF, %rax
 ; LARGE-SMALL-DATA-PIC-NEXT:    addq %rcx, %rax
@@ -914,19 +972,19 @@ define dso_local ptr @lea_global_fn() #0 {
 ;
 ; LARGE-PIC-LABEL: lea_global_fn:
 ; LARGE-PIC:       # %bb.0:
-; LARGE-PIC-NEXT:  .L17$pb:
-; LARGE-PIC-NEXT:    leaq .L17$pb(%rip), %rax
-; LARGE-PIC-NEXT:    movabsq $_GLOBAL_OFFSET_TABLE_-.L17$pb, %rcx
+; LARGE-PIC-NEXT:  .L18$pb:
+; LARGE-PIC-NEXT:    leaq .L18$pb(%rip), %rax
+; LARGE-PIC-NEXT:    movabsq $_GLOBAL_OFFSET_TABLE_-.L18$pb, %rcx
 ; LARGE-PIC-NEXT:    addq %rax, %rcx
 ; LARGE-PIC-NEXT:    movabsq $global_fn@GOTOFF, %rax
 ; LARGE-PIC-NEXT:    addq %rcx, %rax
 ; LARGE-PIC-NEXT:    retq
 ;
 ; LARGE-SMALL-DATA-PIC-LABEL: lea_global_fn:
 ; LARGE-SMALL-DATA-PIC:       # %bb.0:
-; LARGE-SMALL-DATA-PIC-NEXT:  .L17$pb:
-; LARGE-SMALL-DATA-PIC-NEXT:    leaq .L17$pb(%rip), %rax
-; LARGE-SMALL-DATA-PIC-NEXT:    movabsq $_GLOBAL_OFFSET_TABLE_-.L17$pb, %rcx
+; LARGE-SMALL-DATA-PIC-NEXT:  .L18$pb:
+; LARGE-SMALL-DATA-PIC-NEXT:    leaq .L18$pb(%rip), %rax
+; LARGE-SMALL-DATA-PIC-NEXT:    movabsq $_GLOBAL_OFFSET_TABLE_-.L18$pb, %rcx
 ; LARGE-SMALL-DATA-PIC-NEXT:    addq %rax, %rcx
 ; LARGE-SMALL-DATA-PIC-NEXT:    movabsq $global_fn@GOTOFF, %rax
 ; LARGE-SMALL-DATA-PIC-NEXT:    addq %rcx, %rax
@@ -967,19 +1025,19 @@ define dso_local ptr @lea_extern_fn() #0 {
 ;
 ; LARGE-PIC-LABEL: lea_extern_fn:
 ; LARGE-PIC:       # %bb.0:
-; LARGE-PIC-NEXT:  .L18$pb:
-; LARGE-PIC-NEXT:    leaq .L18$pb(%rip), %rax
-; LARGE-PIC-NEXT:    movabsq $_GLOBAL_OFFSET_TABLE_-.L18$pb, %rcx
+; LARGE-PIC-NEXT:  .L19$pb:
+; LARGE-PIC-NEXT:    leaq .L19$pb(%rip), %rax
+; LARGE-PIC-NEXT:    movabsq $_GLOBAL_OFFSET_TABLE_-.L19$pb, %rcx
 ; LARGE-PIC-NEXT:    addq %rax, %rcx
 ; LARGE-PIC-NEXT:    movabsq $extern_fn@GOT, %rax
 ; LARGE-PIC-NEXT:    movq (%rcx,%rax), %rax
 ; LARGE-PIC-NEXT:    retq
 ;
 ; LARGE-SMALL-DATA-PIC-LABEL: lea_extern_fn:
 ; LARGE-SMALL-DATA-PIC:       # %bb.0:
-; LARGE-SMALL-DATA-PIC-NEXT:  .L18$pb:
-; LARGE-SMALL-DATA-PIC-NEXT:    leaq .L18$pb(%rip), %rax
-; LARGE-SMALL-DATA-PIC-NEXT:    movabsq $_GLOBAL_OFFSET_TABLE_-.L18$pb, %rcx
+; LARGE-SMALL-DATA-PIC-NEXT:  .L19$pb:
+; LARGE-SMALL-DATA-PIC-NEXT:    leaq .L19$pb(%rip), %rax
+; LARGE-SMALL-DATA-PIC-NEXT:    movabsq $_GLOBAL_OFFSET_TABLE_-.L19$pb, %rcx
 ; LARGE-SMALL-DATA-PIC-NEXT:    addq %rax, %rcx
 ; LARGE-SMALL-DATA-PIC-NEXT:    movabsq $extern_fn@GOT, %rax
 ; LARGE-SMALL-DATA-PIC-NEXT:    movq (%rcx,%rax), %rax
@@ -1020,19 +1078,19 @@ define dso_local ptr @lea_ifunc() #0 {
 ;
 ; LARGE-PIC-LABEL: lea_ifunc:
 ; LARGE-PIC:       # %bb.0:
-; LARGE-PIC-NEXT:  .L19$pb:
-; LARGE-PIC-NEXT:    leaq .L19$pb(%rip), %rax
-; LARGE-PIC-NEXT:    movabsq $_GLOBAL_OFFSET_TABLE_-.L19$pb, %rcx
+; LARGE-PIC-NEXT:  .L20$pb:
+; LARGE-PIC-NEXT:    leaq .L20$pb(%rip), %rax
+; LARGE-PIC-NEXT:    movabsq $_GLOBAL_OFFSET_TABLE_-.L20$pb, %rcx
 ; LARGE-PIC-NEXT:    addq %rax, %rcx
 ; LARGE-PIC-NEXT:    movabsq $ifunc_func@GOT, %rax
 ; LARGE-PIC-NEXT:    movq (%rcx,%rax), %rax
 ; LARGE-PIC-NEXT:    retq
 ;
 ; LARGE-SMALL-DATA-PIC-LABEL: lea_ifunc:
 ; LARGE-SMALL-DATA-PIC:       # %bb.0:
-; LARGE-SMALL-DATA-PIC-NEXT:  .L19$pb:
-; LARGE-SMALL-DATA-PIC-NEXT:    leaq .L19$pb(%rip), %rax
-; LARGE-SMALL-DATA-PIC-NEXT:    movabsq $_GLOBAL_OFFSET_TABLE_-.L19$pb, %rcx
+; LARGE-SMALL-DATA-PIC-NEXT:  .L20$pb:
+; LARGE-SMALL-DATA-PIC-NEXT:    leaq .L20$pb(%rip), %rax
+; LARGE-SMALL-DATA-PIC-NEXT:    movabsq $_GLOBAL_OFFSET_TABLE_-.L20$pb, %rcx
 ; LARGE-SMALL-DATA-PIC-NEXT:    addq %rax, %rcx
 ; LARGE-SMALL-DATA-PIC-NEXT:    movabsq $ifunc_func@GOT, %rax
 ; LARGE-SMALL-DATA-PIC-NEXT:    movq (%rcx,%rax), %rax
@@ -1073,19 +1131,19 @@ define dso_local ptr @lea_dso_local_ifunc() #0 {
 ;
 ; LARGE-PIC-LABEL: lea_dso_local_ifunc:
 ; LARGE-PIC:       # %bb.0:
-; LARGE-PIC-NEXT:  .L20$pb:
-; LARGE-PIC-NEXT:    leaq .L20$pb(%rip), %rax
-; LARGE-PIC-NEXT:    movabsq $_GLOBAL_OFFSET_TABLE_-.L20$pb, %rcx
+; LARGE-PIC-NEXT:  .L21$pb:
+; LARGE-PIC-NEXT:    leaq .L21$pb(%rip), %rax
+; LARGE-PIC-NEXT:    movabsq $_GLOBAL_OFFSET_TABLE_-.L21$pb, %rcx
 ; LARGE-PIC-NEXT:    addq %rax, %rcx
 ; LARGE-PIC-NEXT:    movabsq $dso_local_ifunc_func@GOTOFF, %rax
 ; LARGE-PIC-NEXT:    addq %rcx, %rax
 ; LARGE-PIC-NEXT:    retq
 ;
 ; LARGE-SMALL-DATA-PIC-LABEL: lea_dso_local_ifunc:
 ; LARGE-SMALL-DATA-PIC:       # %bb.0:
-; LARGE-SMALL-DATA-PIC-NEXT:  .L20$pb:
-; LARGE-SMALL-DATA-PIC-NEXT:    leaq .L20$pb(%rip), %rax
-; LARGE-SMALL-DATA-PIC-NEXT:    movabsq $_GLOBAL_OFFSET_TABLE_-.L20$pb, %rcx
+; LARGE-SMALL-DATA-PIC-NEXT:  .L21$pb:
+; LARGE-SMALL-DATA-PIC-NEXT:    leaq .L21$pb(%rip), %rax
+; LARGE-SMALL-DATA-PIC-NEXT:    movabsq $_GLOBAL_OFFSET_TABLE_-.L21$pb, %rcx
 ; LARGE-SMALL-DATA-PIC-NEXT:    addq %rax, %rcx
 ; LARGE-SMALL-DATA-PIC-NEXT:    movabsq $dso_local_ifunc_func@GOTOFF, %rax
 ; LARGE-SMALL-DATA-PIC-NEXT:    addq %rcx, %rax
@@ -1160,19 +1218,19 @@ define dso_local float @load_constant_pool(float %x) #0 {
 ;
 ; LARGE-PIC-LABEL: load_constant_pool:
 ; LARGE-PIC:       # %bb.0:
-; LARGE-PIC-NEXT:  .L22$pb:
-; LARGE-PIC-NEXT:    leaq .L22$pb(%rip), %rax
-; LARGE-PIC-NEXT:    movabsq $_GLOBAL_OFFSET_TABLE_-.L22$pb, %rcx
+; LARGE-PIC-NEXT:  .L23$pb:
+; LARGE-PIC-NEXT:    leaq .L23$pb(%rip), %rax
+; LARGE-PIC-NEXT:    movabsq $_GLOBAL_OFFSET_TABLE_-.L23$pb, %rcx
 ; LARGE-PIC-NEXT:    addq %rax, %rcx
 ; LARGE-PIC-NEXT:    movabsq ${{\.?LCPI[0-9]+_[0-9]+}}@GOTOFF, %rax
 ; LARGE-PIC-NEXT:    addss (%rcx,%rax), %xmm0
 ; LARGE-PIC-NEXT:    retq
 ;
 ; LARGE-SMALL-DATA-PIC-LABEL: load_constant_pool:
 ; LARGE-SMALL-DATA-PIC:       # %bb.0:
-; LARGE-SMALL-DATA-PIC-NEXT:  .L22$pb:
-; LARGE-SMALL-DATA-PIC-NEXT:    leaq .L22$pb(%rip), %rax
-; LARGE-SMALL-DATA-PIC-NEXT:    movabsq $_GLOBAL_OFFSET_TABLE_-.L22$pb, %rcx
+; LARGE-SMALL-DATA-PIC-NEXT:  .L23$pb:
+; LARGE-SMALL-DATA-PIC-NEXT:    leaq .L23$pb(%rip), %rax
+; LARGE-SMALL-DATA-PIC-NEXT:    movabsq $_GLOBAL_OFFSET_TABLE_-.L23$pb, %rcx
 ; LARGE-SMALL-DATA-PIC-NEXT:    addq %rax, %rcx
 ; LARGE-SMALL-DATA-PIC-NEXT:    movabsq ${{\.?LCPI[0-9]+_[0-9]+}}@GOTOFF, %rax
 ; LARGE-SMALL-DATA-PIC-NEXT:    addss (%rcx,%rax), %xmm0
