[InstCombine] Pre-commit of test case showing miscompile bug in canEvaluateShuffled

Adding the reproducer from  https://bugs.llvm.org/show_bug.cgi?id=43689,
showing that instcombine is doing a bad transform. It transforms

  %0 = insertelement <2 x i16> undef, i16 %a, i32 0
  %1 = srem <2 x i16> %0, <i16 2, i16 1>
  %2 = shufflevector <2 x i16> %1, <2 x i16> undef, <2 x i32> <i32 undef, i32 0>

into

   %1 = insertelement <2 x i16> undef, i16 %a, i32 1
   %2 = srem <2 x i16> %1, <i16 undef, i16 2>

The undef denominator makes the whole srem undefined.

llvm-svn: 375207

1 files changed, 101 insertions, 0 deletions

diff --git a/llvm/test/Transforms/InstCombine/shufflevector-div-rem.ll b/llvm/test/Transforms/InstCombine/shufflevector-div-rem.ll
new file mode 100644
index 00000000000..ee63a25653b
--- /dev/null
+++ b/llvm/test/Transforms/InstCombine/shufflevector-div-rem.ll
@@ -0,0 +1,101 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt < %s -instcombine -S -o - | FileCheck %s
+
+; This test case was added as a reproducer for a miscompile, where instcombine
+; introduced an
+;   srem <2 x i16> %1, <i16 undef, i16 2>
+; instruction, which makes the whole srem undefined (even if we only end up
+; extracting the second element in the vector).
+define i16 @test_srem_orig(i16 %a, i1 %cmp) {
+; CHECK-LABEL: @test_srem_orig(
+; CHECK-NEXT:    ret i16 1
+;
+  %splatinsert = insertelement <2 x i16> undef, i16 %a, i32 0
+  %splat = shufflevector <2 x i16> %splatinsert, <2 x i16> undef, <2 x i32> zeroinitializer
+  %t1 = select i1 %cmp, <2 x i16> <i16 1, i16 1>, <2 x i16> %splat
+  %t2 = srem <2 x i16> %t1, <i16 2, i16 2>
+  %t3 = extractelement <2 x i16> %t2, i32 1
+  ret i16 %t3
+}
+
+; This is basically a reduced version of test_srem_orig (based on what the
+; code would look like after a few iterations of instcombine, just before we
+; try to transform the shufflevector by doing
+; "evaluateInDifferentElementOrder".
+define <2 x i16> @test_srem(i16 %a, i1 %cmp) {
+; CHECK-LABEL: @test_srem(
+; CHECK-NEXT:    ret <2 x i16> <i16 77, i16 99>
+;
+  %splatinsert = insertelement <2 x i16> undef, i16 %a, i32 0
+  %t1 = srem <2 x i16> %splatinsert, <i16 2, i16 1>
+  %splat.op = shufflevector <2 x i16> %t1, <2 x i16> undef, <2 x i32> <i32 undef, i32 0>
+  %t2 = select i1 %cmp, <2 x i16> <i16 77, i16 99>, <2 x i16> %splat.op
+  ret <2 x i16> %t2
+}
+
+define <2 x i16> @test_urem(i16 %a, i1 %cmp) {
+; CHECK-LABEL: @test_urem(
+; CHECK-NEXT:    ret <2 x i16> <i16 77, i16 99>
+;
+  %splatinsert = insertelement <2 x i16> undef, i16 %a, i32 0
+  %t1 = urem <2 x i16> %splatinsert, <i16 3, i16 1>
+  %splat.op = shufflevector <2 x i16> %t1, <2 x i16> undef, <2 x i32> <i32 undef, i32 0>
+  %t2 = select i1 %cmp, <2 x i16> <i16 77, i16 99>, <2 x i16> %splat.op
+  ret <2 x i16> %t2
+}
+
+define <2 x i16> @test_sdiv(i16 %a, i1 %cmp) {
+; CHECK-LABEL: @test_sdiv(
+; CHECK-NEXT:    ret <2 x i16> <i16 77, i16 99>
+;
+  %splatinsert = insertelement <2 x i16> undef, i16 %a, i32 0
+  %t1 = sdiv <2 x i16> %splatinsert, <i16 2, i16 1>
+  %splat.op = shufflevector <2 x i16> %t1, <2 x i16> undef, <2 x i32> <i32 undef, i32 0>
+  %t2 = select i1 %cmp, <2 x i16> <i16 77, i16 99>, <2 x i16> %splat.op
+  ret <2 x i16> %t2
+}
+
+define <2 x i16> @test_udiv(i16 %a, i1 %cmp) {
+; CHECK-LABEL: @test_udiv(
+; CHECK-NEXT:    ret <2 x i16> <i16 77, i16 99>
+;
+  %splatinsert = insertelement <2 x i16> undef, i16 %a, i32 0
+  %t1 = udiv <2 x i16> %splatinsert, <i16 3, i16 1>
+  %splat.op = shufflevector <2 x i16> %t1, <2 x i16> undef, <2 x i32> <i32 undef, i32 0>
+  %t2 = select i1 %cmp, <2 x i16> <i16 77, i16 99>, <2 x i16> %splat.op
+  ret <2 x i16> %t2
+}
+
+; For fdiv we do not need to worry about div by undef. Verify that the
+; shufflevector is eliminated here.
+define <2 x float> @test_fdiv(float %a, float %b, i1 %cmp) {
+; CHECK-LABEL: @test_fdiv(
+; CHECK-NEXT:    [[TMP1:%.*]] = insertelement <2 x float> undef, float [[A:%.*]], i32 1
+; CHECK-NEXT:    [[TMP2:%.*]] = fdiv <2 x float> [[TMP1]], <float undef, float 3.000000e+00>
+; CHECK-NEXT:    [[T2:%.*]] = select i1 [[CMP:%.*]], <2 x float> <float 7.700000e+01, float 9.900000e+01>, <2 x float> [[TMP2]]
+; CHECK-NEXT:    ret <2 x float> [[T2]]
+;
+  %splatinsert = insertelement <2 x float> undef, float %a, i32 0
+  %denom = insertelement <2 x float> <float 3.0, float undef>, float 1.0, i32 1
+  %t1 = fdiv <2 x float> %splatinsert, %denom
+  %splat.op = shufflevector <2 x float> %t1, <2 x float> undef, <2 x i32> <i32 undef, i32 0>
+  %t2 = select i1 %cmp, <2 x float> <float 77.0, float 99.0>, <2 x float> %splat.op
+  ret <2 x float> %t2
+}
+
+; For frem we do not need to worry about div by undef. Verify that the
+; shufflevector is eliminated here.
+define <2 x float> @test_frem(float %a, float %b, i1 %cmp) {
+; CHECK-LABEL: @test_frem(
+; CHECK-NEXT:    [[TMP1:%.*]] = insertelement <2 x float> undef, float [[A:%.*]], i32 1
+; CHECK-NEXT:    [[TMP2:%.*]] = frem <2 x float> [[TMP1]], <float undef, float 3.000000e+00>
+; CHECK-NEXT:    [[T2:%.*]] = select i1 [[CMP:%.*]], <2 x float> <float 7.700000e+01, float 9.900000e+01>, <2 x float> [[TMP2]]
+; CHECK-NEXT:    ret <2 x float> [[T2]]
+;
+  %splatinsert = insertelement <2 x float> undef, float %a, i32 0
+  %denom = insertelement <2 x float> <float 3.0, float undef>, float 1.0, i32 1
+  %t1 = frem <2 x float> %splatinsert, %denom
+  %splat.op = shufflevector <2 x float> %t1, <2 x float> undef, <2 x i32> <i32 undef, i32 0>
+  %t2 = select i1 %cmp, <2 x float> <float 77.0, float 99.0>, <2 x float> %splat.op
+  ret <2 x float> %t2
+}