[PATCH] D34974: [InstCombine] Add single use checks to SimplifyBSwap to ensure we are really saving instructions

[Craig Topper via Phabricator via llvm-commits]

craig.topper created this revision.

Bswap isn't a simple operation so we need to make sure we are really removing a call to it before doing these simplifications.

For the case when both LHS and RHS are bswaps I've allowed it to be moved if either LHS or RHS has a single use since that at least allows us to move it later where it might find another bswap to combine with and it decreases the use count on the other side so maybe the other user can be optimized.


https://reviews.llvm.org/D34974

Files:
  lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
  test/Transforms/InstCombine/bswap-fold.ll


Index: test/Transforms/InstCombine/bswap-fold.ll
===================================================================
--- test/Transforms/InstCombine/bswap-fold.ll
+++ test/Transforms/InstCombine/bswap-fold.ll
@@ -285,9 +285,8 @@
 ; CHECK-LABEL: @bs_and64_multiuse1(
 ; CHECK-NEXT:    [[TMP1:%.*]] = tail call i64 @llvm.bswap.i64(i64 [[A:%.*]])
 ; CHECK-NEXT:    [[TMP2:%.*]] = tail call i64 @llvm.bswap.i64(i64 [[B:%.*]])
-; CHECK-NEXT:    [[TMP1:%.*]] = and i64 [[A]], [[B]]
-; CHECK-NEXT:    [[TMP2:%.*]] = call i64 @llvm.bswap.i64(i64 [[TMP1]])
-; CHECK-NEXT:    [[TMP4:%.*]] = mul i64 [[TMP2]], [[TMP1]]
+; CHECK-NEXT:    [[TMP3:%.*]] = and i64 [[TMP1]], [[TMP2]]
+; CHECK-NEXT:    [[TMP4:%.*]] = mul i64 [[TMP3]], [[TMP1]]
 ; CHECK-NEXT:    [[TMP5:%.*]] = mul i64 [[TMP4]], [[TMP2]]
 ; CHECK-NEXT:    ret i64 [[TMP5]]
 ;
@@ -332,8 +331,7 @@
 define i64 @bs_and64i_multiuse(i64 %a, i64 %b) #0 {
 ; CHECK-LABEL: @bs_and64i_multiuse(
 ; CHECK-NEXT:    [[TMP1:%.*]] = tail call i64 @llvm.bswap.i64(i64 [[A:%.*]])
-; CHECK-NEXT:    [[TMP1:%.*]] = and i64 [[A]], 129085117527228416
-; CHECK-NEXT:    [[TMP2:%.*]] = call i64 @llvm.bswap.i64(i64 [[TMP1]])
+; CHECK-NEXT:    [[TMP2:%.*]] = and i64 [[TMP1]], 1000000001
 ; CHECK-NEXT:    [[TMP3:%.*]] = mul i64 [[TMP2]], [[TMP1]]
 ; CHECK-NEXT:    ret i64 [[TMP3]]
 ;
Index: lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
===================================================================
--- lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
+++ lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
@@ -82,20 +82,25 @@
 Value *InstCombiner::SimplifyBSwap(BinaryOperator &I) {
   assert(I.isBitwiseLogicOp() && "Unexpected opcode for bswap simplifying");
 
-  // TODO We should probably check for single use of the bswap.
+  Value *OldLHS = I.getOperand(0);
+  Value *OldRHS = I.getOperand(1);
 
   Value *NewLHS;
-  if (!match(I.getOperand(0), m_BSwap(m_Value(NewLHS))))
+  if (!match(OldLHS, m_BSwap(m_Value(NewLHS))))
     return nullptr;
 
   Value *NewRHS;
   const APInt *C;
 
-  if (match(I.getOperand(1), m_BSwap(m_Value(NewRHS)))) {
+  if (match(OldRHS, m_BSwap(m_Value(NewRHS)))) {
     // OP( BSWAP(x), BSWAP(y) ) -> BSWAP( OP(x, y) )
+    if (!OldLHS->hasOneUse() && !OldRHS->hasOneUse())
+      return nullptr;
     // NewRHS initialized by the matcher.
-  } else if (match(I.getOperand(1), m_APInt(C))) {
+  } else if (match(OldRHS, m_APInt(C))) {
     // OP( BSWAP(x), CONSTANT ) -> BSWAP( OP(x, BSWAP(CONSTANT) ) )
+    if (!OldLHS->hasOneUse())
+      return nullptr;
     NewRHS = ConstantInt::get(I.getType(), C->byteSwap());
   } else
     return nullptr;


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