[PATCH] D45537: [CodeGenPrepare] Move Extension Instructions Through Logical And Shift Instructions

[Quentin Colombet via Phabricator via llvm-commits]

qcolombet added inline comments.


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Comment at: lib/CodeGen/CodeGenPrepare.cpp:3369
+       Inst->getOpcode() == Instruction::Or) &&
+      isa<ConstantInt>(Inst->getOperand(1)))
+    return true;
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Do we need to restrict this to constants?


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Comment at: lib/CodeGen/CodeGenPrepare.cpp:3382
+  if (Inst->getOpcode() == Instruction::LShr &&
+      isa<ConstantInt>(Inst->getOperand(1)) && !IsSExt)
+    return true;
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Same question as And and Or, do we need to restrict to constant?
More generally, I am not an expert on how we are dealing with poisioned value, but we probably want to call out (in a comment) that given we don't have the nuw flag, we may change a poisioned value into a regular value (eg., zext i32(shrl i8 %val, 12) => gives poison, but shrl i32 (zext i8 %val), 12 is totally fine. I believe this is okay because undef also covers valid value.


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Comment at: lib/CodeGen/CodeGenPrepare.cpp:3386
+  // and(ext(shl(opnd, cst)), cst) --> and(shl(ext(opnd), ext(cst)), cst)
+  if (Inst->getOpcode() == Instruction::Shl && Inst->hasOneUse() &&
+      isa<ConstantInt>(Inst->getOperand(1))) {
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Same comment as the previous one.


https://reviews.llvm.org/D45537