[PowerPC] Fix SH field overflow issue

Store rlwinm Rx, Ry, 32, 0, 31 as rlwinm Rx, Ry, 0, 0, 31 and store
rldicl Rx, Ry, 64, 0 as rldicl Rx, Ry, 0, 0. Otherwise SH field is overflow and
fails assertion in assembly printing stage.

Differential Revision: https://reviews.llvm.org/D66991

llvm-svn: 373519

Author: Yi-Hong Lyu

llvm/lib/Target/PowerPC/PPCInstrInfo.cpp

@@ -3571,16 +3571,20 @@ bool PPCInstrInfo::transformToImmFormFedByLI(MachineInstr &MI,
       } else {
         // The 32 bit and 64 bit instructions are quite different.
         if (SpecialShift32) {
-          // Left shifts use (N, 0, 31-N), right shifts use (32-N, N, 31).
-          uint64_t SH = RightShift ? 32 - ShAmt : ShAmt;
+          // Left shifts use (N, 0, 31-N).
+          // Right shifts use (32-N, N, 31) if 0 < N < 32.
+          //              use (0, 0, 31)    if N == 0.
+          uint64_t SH = ShAmt == 0 ? 0 : RightShift ? 32 - ShAmt : ShAmt;
           uint64_t MB = RightShift ? ShAmt : 0;
           uint64_t ME = RightShift ? 31 : 31 - ShAmt;
           replaceInstrOperandWithImm(MI, III.OpNoForForwarding, SH);
           MachineInstrBuilder(*MI.getParent()->getParent(), MI).addImm(MB)
             .addImm(ME);
         } else {
-          // Left shifts use (N, 63-N), right shifts use (64-N, N).
-          uint64_t SH = RightShift ? 64 - ShAmt : ShAmt;
+          // Left shifts use (N, 63-N).
+          // Right shifts use (64-N, N) if 0 < N < 64.
+          //              use (0, 0)    if N == 0.
+          uint64_t SH = ShAmt == 0 ? 0 : RightShift ? 64 - ShAmt : ShAmt;
           uint64_t ME = RightShift ? ShAmt : 63 - ShAmt;
           replaceInstrOperandWithImm(MI, III.OpNoForForwarding, SH);
           MachineInstrBuilder(*MI.getParent()->getParent(), MI).addImm(ME);

llvm/test/CodeGen/PowerPC/sh-overflow.mir

@@ -0,0 +1,58 @@
+# RUN: llc -O3 -mtriple=powerpc64le-unknown-linux-gnu -start-after ppc-mi-peepholes -ppc-late-peephole -ppc-asm-full-reg-names -verify-machineinstrs %s -o - | FileCheck %s
+
+---
+name:            special_right_shift32_0
+alignment:       2
+tracksRegLiveness: true
+registers:
+  - { id: 0, class: gprc }
+  - { id: 1, class: gprc }
+  - { id: 2, class: gprc }
+liveins:
+  - { reg: '$r3', virtual-reg: '%0' }
+machineFunctionInfo: {}
+body:             |
+  bb.0.entry:
+    liveins: $r3
+
+    ; Ensure we do not attempt to transform this into srwi $r3, $r3, 0 in the
+    ; form specified by ISA 3.0b (rlwinm $r3, $r3, 32 - 0, 0, 31)
+
+    ; CHECK-LABEL: special_right_shift32_0:
+    ; CHECK:         slwi r[[#]], r[[#]], 0
+
+    %0:gprc = COPY killed $r3
+    %1:gprc = LI 0
+    %2:gprc = SRW killed %0, killed %1
+    $r3 = COPY killed %2
+    BLR implicit $lr, implicit $rm, implicit killed $r3
+
+...
+---
+name:            special_right_shift64_0
+alignment:       2
+tracksRegLiveness: true
+registers:
+  - { id: 0, class: g8rc }
+  - { id: 1, class: gprc }
+  - { id: 2, class: g8rc }
+liveins:
+  - { reg: '$x3', virtual-reg: '%0' }
+machineFunctionInfo: {}
+body:             |
+  bb.0.entry:
+    liveins: $x3
+
+    ; Ensure we do not attempt to transform this into srdi $r3, $r3, 0 in the
+    ; form specified by ISA 3.0b (rldicl $r3, $r3, 64 - 0, 0)
+
+    ; CHECK-LABEL: special_right_shift64_0:
+    ; CHECK:         rotldi r[[#]], r[[#]], 0
+
+    %0:g8rc = COPY killed $x3
+    %1:gprc = LI 0
+    %2:g8rc = SRD killed %0, killed %1
+    $x3 = COPY killed %2
+    BLR8 implicit $lr8, implicit $rm, implicit killed $x3
+
+...