[InstCombine] fold ldexp(x, sext(i1 y)) to fmul x, (select y, 0.5, 1.0) (#95073)

Follow up of #94887.

Context:
#94887 (review)

Author: c8ef

llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp

@@ -2619,6 +2619,7 @@ Instruction *InstCombinerImpl::visitCallInst(CallInst &CI) {
     }
 
     // ldexp(x, zext(i1 y)) -> fmul x, (select y, 2.0, 1.0)
+    // ldexp(x, sext(i1 y)) -> fmul x, (select y, 0.5, 1.0)
     Value *ExtSrc;
     if (match(Exp, m_ZExt(m_Value(ExtSrc))) &&
         ExtSrc->getType()->getScalarSizeInBits() == 1) {
@@ -2627,6 +2628,13 @@ Instruction *InstCombinerImpl::visitCallInst(CallInst &CI) {
                                ConstantFP::get(II->getType(), 1.0));
       return BinaryOperator::CreateFMulFMF(Src, Select, II);
     }
+    if (match(Exp, m_SExt(m_Value(ExtSrc))) &&
+        ExtSrc->getType()->getScalarSizeInBits() == 1) {
+      Value *Select =
+          Builder.CreateSelect(ExtSrc, ConstantFP::get(II->getType(), 0.5),
+                               ConstantFP::get(II->getType(), 1.0));
+      return BinaryOperator::CreateFMulFMF(Src, Select, II);
+    }
 
     break;
   }

llvm/test/Transforms/InstCombine/ldexp-zext.ll renamed to llvm/test/Transforms/InstCombine/ldexp-ext.ll

@@ -55,3 +55,58 @@ define <2 x float> @ldexp_zext_float_vector(<2 x float> %x, <2 x i1> %bool) {
   %ldexp = call <2 x float> @llvm.ldexp.v2f32.v2i32(<2 x float> %x, <2 x i32> %zext)
   ret <2 x float> %ldexp
 }
+
+define float @ldexp_sext_float(float %x, i1 %bool) {
+; CHECK-LABEL: @ldexp_sext_float(
+; CHECK-NEXT:    [[TMP1:%.*]] = select i1 [[BOOL:%.*]], float 5.000000e-01, float 1.000000e+00
+; CHECK-NEXT:    [[LDEXP:%.*]] = fmul float [[TMP1]], [[X:%.*]]
+; CHECK-NEXT:    ret float [[LDEXP]]
+;
+  %sext = sext i1 %bool to i32
+  %ldexp = call float @llvm.ldexp.f32.i32(float %x, i32 %sext)
+  ret float %ldexp
+}
+
+define float @ldexp_sext_float_negative(float %x, i8 %y) {
+; CHECK-LABEL: @ldexp_sext_float_negative(
+; CHECK-NEXT:    [[SEXT:%.*]] = sext i8 [[Y:%.*]] to i32
+; CHECK-NEXT:    [[LDEXP:%.*]] = call float @llvm.ldexp.f32.i32(float [[X:%.*]], i32 [[SEXT]])
+; CHECK-NEXT:    ret float [[LDEXP]]
+;
+  %sext = sext i8 %y to i32
+  %ldexp = call float @llvm.ldexp.f32.i32(float %x, i32 %sext)
+  ret float %ldexp
+}
+
+define double @ldexp_sext_double(double %x, i1 %bool) {
+; CHECK-LABEL: @ldexp_sext_double(
+; CHECK-NEXT:    [[TMP1:%.*]] = select i1 [[BOOL:%.*]], double 5.000000e-01, double 1.000000e+00
+; CHECK-NEXT:    [[LDEXP:%.*]] = fmul double [[TMP1]], [[X:%.*]]
+; CHECK-NEXT:    ret double [[LDEXP]]
+;
+  %sext = sext i1 %bool to i32
+  %ldexp = call double @llvm.ldexp.f64.i32(double %x, i32 %sext)
+  ret double %ldexp
+}
+
+define double @ldexp_sext_double_fast_math(double %x, i1 %bool) {
+; CHECK-LABEL: @ldexp_sext_double_fast_math(
+; CHECK-NEXT:    [[TMP1:%.*]] = select i1 [[BOOL:%.*]], double 5.000000e-01, double 1.000000e+00
+; CHECK-NEXT:    [[LDEXP:%.*]] = fmul reassoc double [[TMP1]], [[X:%.*]]
+; CHECK-NEXT:    ret double [[LDEXP]]
+;
+  %sext = sext i1 %bool to i32
+  %ldexp = call reassoc double @llvm.ldexp.f64.i32(double %x, i32 %sext)
+  ret double %ldexp
+}
+
+define <2 x float> @ldexp_sext_float_vector(<2 x float> %x, <2 x i1> %bool) {
+; CHECK-LABEL: @ldexp_sext_float_vector(
+; CHECK-NEXT:    [[TMP1:%.*]] = select <2 x i1> [[BOOL:%.*]], <2 x float> <float 5.000000e-01, float 5.000000e-01>, <2 x float> <float 1.000000e+00, float 1.000000e+00>
+; CHECK-NEXT:    [[LDEXP:%.*]] = fmul <2 x float> [[TMP1]], [[X:%.*]]
+; CHECK-NEXT:    ret <2 x float> [[LDEXP]]
+;
+  %sext = sext <2 x i1> %bool to <2 x i32>
+  %ldexp = call <2 x float> @llvm.ldexp.v2f32.v2i32(<2 x float> %x, <2 x i32> %sext)
+  ret <2 x float> %ldexp
+}