[llvm-branch-commits] [llvm] 94ead01 - [InstCombine] Improve vector undef handling for sext(ashr(shl(trunc()))) fold, 2

[Roman Lebedev via llvm-branch-commits]

Author: Roman Lebedev
Date: 2020-12-01T16:54:00+03:00
New Revision: 94ead0190ff18be337c5c84abccc315fd68f41fc

URL: https://github.com/llvm/llvm-project/commit/94ead0190ff18be337c5c84abccc315fd68f41fc
DIFF: https://github.com/llvm/llvm-project/commit/94ead0190ff18be337c5c84abccc315fd68f41fc.diff

LOG: [InstCombine] Improve vector undef handling for sext(ashr(shl(trunc()))) fold, 2

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
    llvm/test/Transforms/InstCombine/trunc.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 319c07d9f8a9..ebab23a19525 100644
--- a/llvm/test/Transforms/InstCombine/sext.ll
+++ b/llvm/test/Transforms/InstCombine/sext.ll
@@ -167,10 +167,8 @@ 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>
@@ -181,10 +179,8 @@ 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>
@@ -195,8 +191,8 @@ 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>

diff  --git a/llvm/test/Transforms/InstCombine/trunc.ll b/llvm/test/Transforms/InstCombine/trunc.ll
index d9b02eaa1698..fc13d86bcfc3 100644
--- a/llvm/test/Transforms/InstCombine/trunc.ll
+++ b/llvm/test/Transforms/InstCombine/trunc.ll
@@ -114,8 +114,8 @@ define <2 x i64> @test2_vec_nonuniform(<2 x i64> %a) {
 define <2 x i64> @test2_vec_undef(<2 x i64> %a) {
 ; CHECK-LABEL: @test2_vec_undef(
 ; CHECK-NEXT:    [[B:%.*]] = trunc <2 x i64> [[A:%.*]] to <2 x i32>
-; CHECK-NEXT:    [[D1:%.*]] = shl <2 x i64> [[A]], <i64 36, i64 0>
-; CHECK-NEXT:    [[D:%.*]] = ashr <2 x i64> [[D1]], <i64 36, i64 0>
+; CHECK-NEXT:    [[D1:%.*]] = shl <2 x i64> [[A]], <i64 36, i64 undef>
+; CHECK-NEXT:    [[D:%.*]] = ashr <2 x i64> [[D1]], <i64 36, i64 undef>
 ; CHECK-NEXT:    call void @use_vec(<2 x i32> [[B]])
 ; CHECK-NEXT:    ret <2 x i64> [[D]]
 ;