[llvm-branch-commits] [llvm] aa1aa13 - [InstCombine] Improve vector undef handling for sext(ashr(shl(trunc()))) fold

[Roman Lebedev via llvm-branch-commits]

Author: Roman Lebedev
Date: 2020-12-01T15:13:08+03:00
New Revision: aa1aa135097ecfab6d9917a435142030eff0a226

URL: https://github.com/llvm/llvm-project/commit/aa1aa135097ecfab6d9917a435142030eff0a226
DIFF: https://github.com/llvm/llvm-project/commit/aa1aa135097ecfab6d9917a435142030eff0a226.diff

LOG: [InstCombine] Improve vector undef handling for sext(ashr(shl(trunc()))) fold

If the shift amount was undef for some lane, the shift amount in opposite
shift is irrelevant for that lane, and the new shift amount for that lane
can be undef.

Added: 
    

Modified: 
    llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
    llvm/test/Transforms/InstCombine/sext.ll

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
index 59dae932ae49..6e94e5823433 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
@@ -1520,13 +1520,15 @@ Instruction *InstCombinerImpl::visitSExt(SExtInst &CI) {
   Constant *BA = nullptr, *CA = nullptr;
   if (match(Src, m_AShr(m_Shl(m_Trunc(m_Value(A)), m_Constant(BA)),
                         m_Constant(CA))) &&
-      BA == CA && A->getType() == DestTy) {
+      BA->isElementWiseEqual(CA) && A->getType() == DestTy) {
     Constant *WideCurrShAmt = ConstantExpr::getSExt(CA, DestTy);
     Constant *NumLowbitsLeft = ConstantExpr::getSub(
         ConstantInt::get(DestTy, SrcTy->getScalarSizeInBits()), WideCurrShAmt);
     Constant *NewShAmt = ConstantExpr::getSub(
         ConstantInt::get(DestTy, DestTy->getScalarSizeInBits()),
         NumLowbitsLeft);
+    NewShAmt =
+        Constant::mergeUndefsWith(Constant::mergeUndefsWith(NewShAmt, BA), CA);
     A = Builder.CreateShl(A, NewShAmt, CI.getName());
     return BinaryOperator::CreateAShr(A, NewShAmt);
   }

diff  --git a/llvm/test/Transforms/InstCombine/sext.ll b/llvm/test/Transforms/InstCombine/sext.ll
index 23639e9d9bf6..31923fd70597 100644
--- a/llvm/test/Transforms/InstCombine/sext.ll
+++ b/llvm/test/Transforms/InstCombine/sext.ll
@@ -166,10 +166,8 @@ define <2 x i32> @test10_vec_nonuniform(<2 x i32> %i) {
 
 define <2 x i32> @test10_vec_undef0(<2 x i32> %i) {
 ; CHECK-LABEL: @test10_vec_undef0(
-; CHECK-NEXT:    [[A:%.*]] = trunc <2 x i32> [[I:%.*]] to <2 x i8>
-; CHECK-NEXT:    [[B:%.*]] = shl <2 x i8> [[A]], <i8 6, i8 0>
-; CHECK-NEXT:    [[C:%.*]] = ashr <2 x i8> [[B]], <i8 6, i8 undef>
-; CHECK-NEXT:    [[D:%.*]] = sext <2 x i8> [[C]] to <2 x i32>
+; CHECK-NEXT:    [[D1:%.*]] = shl <2 x i32> [[I:%.*]], <i32 30, i32 undef>
+; CHECK-NEXT:    [[D:%.*]] = ashr <2 x i32> [[D1]], <i32 30, i32 undef>
 ; CHECK-NEXT:    ret <2 x i32> [[D]]
 ;
   %A = trunc <2 x i32> %i to <2 x i8>
@@ -180,10 +178,8 @@ define <2 x i32> @test10_vec_undef0(<2 x i32> %i) {
 }
 define <2 x i32> @test10_vec_undef1(<2 x i32> %i) {
 ; CHECK-LABEL: @test10_vec_undef1(
-; CHECK-NEXT:    [[A:%.*]] = trunc <2 x i32> [[I:%.*]] to <2 x i8>
-; CHECK-NEXT:    [[B:%.*]] = shl <2 x i8> [[A]], <i8 6, i8 undef>
-; CHECK-NEXT:    [[C:%.*]] = ashr <2 x i8> [[B]], <i8 6, i8 0>
-; CHECK-NEXT:    [[D:%.*]] = sext <2 x i8> [[C]] to <2 x i32>
+; CHECK-NEXT:    [[D1:%.*]] = shl <2 x i32> [[I:%.*]], <i32 30, i32 undef>
+; CHECK-NEXT:    [[D:%.*]] = ashr <2 x i32> [[D1]], <i32 30, i32 undef>
 ; CHECK-NEXT:    ret <2 x i32> [[D]]
 ;
   %A = trunc <2 x i32> %i to <2 x i8>
@@ -194,8 +190,8 @@ define <2 x i32> @test10_vec_undef1(<2 x i32> %i) {
 }
 define <2 x i32> @test10_vec_undef2(<2 x i32> %i) {
 ; CHECK-LABEL: @test10_vec_undef2(
-; CHECK-NEXT:    [[D1:%.*]] = shl <2 x i32> [[I:%.*]], <i32 30, i32 24>
-; CHECK-NEXT:    [[D:%.*]] = ashr <2 x i32> [[D1]], <i32 30, i32 24>
+; CHECK-NEXT:    [[D1:%.*]] = shl <2 x i32> [[I:%.*]], <i32 30, i32 undef>
+; CHECK-NEXT:    [[D:%.*]] = ashr <2 x i32> [[D1]], <i32 30, i32 undef>
 ; CHECK-NEXT:    ret <2 x i32> [[D]]
 ;
   %A = trunc <2 x i32> %i to <2 x i8>