[llvm] 1c040a3 - [InstCombine] commonShiftTransforms - add support for pow2 nonuniform constant vectors in srem fold

[Simon Pilgrim via llvm-commits]

Author: Simon Pilgrim
Date: 2020-10-09T15:59:33+01:00
New Revision: 1c040a3e5615e54022cf9786b0f5c440ae3d3205

URL: https://github.com/llvm/llvm-project/commit/1c040a3e5615e54022cf9786b0f5c440ae3d3205
DIFF: https://github.com/llvm/llvm-project/commit/1c040a3e5615e54022cf9786b0f5c440ae3d3205.diff

LOG: [InstCombine] commonShiftTransforms - add support for pow2 nonuniform constant vectors in srem fold

Note: we already fold srem to undef if any denominator vector element is undef.

Added: 
    

Modified: 
    llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp
    llvm/test/Transforms/InstCombine/shift.ll

Removed: 
    


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diff  --git a/llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp b/llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp
index 828002f44d42..627e3390ea14 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp
@@ -402,15 +402,15 @@ Instruction *InstCombinerImpl::commonShiftTransforms(BinaryOperator &I) {
       return BinaryOperator::Create(
           I.getOpcode(), Builder.CreateBinOp(I.getOpcode(), Op0, C), A);
 
-  // X shift (A srem B) -> X shift (A and B-1) iff B is a power of 2.
+  // X shift (A srem C) -> X shift (A and (C - 1)) iff C is a power of 2.
   // Because shifts by negative values (which could occur if A were negative)
   // are undefined.
-  const APInt *B;
-  if (Op1->hasOneUse() && match(Op1, m_SRem(m_Value(A), m_Power2(B)))) {
+  if (Op1->hasOneUse() && match(Op1, m_SRem(m_Value(A), m_Constant(C))) &&
+      match(C, m_Power2())) {
     // FIXME: Should this get moved into SimplifyDemandedBits by saying we don't
     // demand the sign bit (and many others) here??
-    Value *Rem = Builder.CreateAnd(A, ConstantInt::get(I.getType(), *B - 1),
-                                   Op1->getName());
+    Constant *Mask = ConstantExpr::getSub(C, ConstantInt::get(I.getType(), 1));
+    Value *Rem = Builder.CreateAnd(A, Mask, Op1->getName());
     return replaceOperand(I, 1, Rem);
   }
 

diff  --git a/llvm/test/Transforms/InstCombine/shift.ll b/llvm/test/Transforms/InstCombine/shift.ll
index 18aac5ac44b0..70ef9c54c1f6 100644
--- a/llvm/test/Transforms/InstCombine/shift.ll
+++ b/llvm/test/Transforms/InstCombine/shift.ll
@@ -616,8 +616,8 @@ define <2 x i32> @test38_uniform(<2 x i32> %x) nounwind readnone {
 
 define <3 x i32> @test38_nonuniform(<3 x i32> %x) nounwind readnone {
 ; CHECK-LABEL: @test38_nonuniform(
-; CHECK-NEXT:    [[REM:%.*]] = srem <3 x i32> [[X:%.*]], <i32 32, i32 16, i32 1>
-; CHECK-NEXT:    [[SHL:%.*]] = shl <3 x i32> <i32 1, i32 1, i32 1>, [[REM]]
+; CHECK-NEXT:    [[REM1:%.*]] = and <3 x i32> [[X:%.*]], <i32 31, i32 15, i32 0>
+; CHECK-NEXT:    [[SHL:%.*]] = shl <3 x i32> <i32 1, i32 1, i32 1>, [[REM1]]
 ; CHECK-NEXT:    ret <3 x i32> [[SHL]]
 ;
   %rem = srem <3 x i32> %x, <i32 32, i32 16, i32 1>