[PATCH] D31552: [InstCombine] Teach SimplifyDemandedInstructionBits that even if we reach an instruction that has multiple uses, if we know all the bits for the demanded bits for this context we can go ahead and create a constant.

[Phabricator via Phabricator via llvm-commits]

This revision was automatically updated to reflect the committed changes.
Closed by commit rL300084: [InstCombine] Teach SimplifyDemandedInstructionBits that even if we reach an… (authored by ctopper).

Changed prior to commit:
  https://reviews.llvm.org/D31552?vs=93713&id=95007#toc

Repository:
  rL LLVM

https://reviews.llvm.org/D31552

Files:
  llvm/trunk/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
  llvm/trunk/test/Transforms/InstCombine/and2.ll


Index: llvm/trunk/test/Transforms/InstCombine/and2.ll
===================================================================
--- llvm/trunk/test/Transforms/InstCombine/and2.ll
+++ llvm/trunk/test/Transforms/InstCombine/and2.ll
@@ -171,7 +171,7 @@
 define i32 @test14(i32 %a, i32 %b) {
 ; CHECK-LABEL: @test14(
 ; CHECK-NEXT:    [[X:%.*]] = shl i32 [[A:%.*]], 8
-; CHECK-NEXT:    [[Y:%.*]] = sub i32 [[X]], [[B:%.*]]
+; CHECK-NEXT:    [[Y:%.*]] = sub i32 0, [[B:%.*]]
 ; CHECK-NEXT:    [[Z:%.*]] = and i32 [[Y]], 128
 ; CHECK-NEXT:    [[W:%.*]] = mul i32 [[Z]], [[X]]
 ; CHECK-NEXT:    ret i32 [[W]]
Index: llvm/trunk/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
===================================================================
--- llvm/trunk/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
+++ llvm/trunk/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
@@ -834,6 +834,12 @@
 
   // Compute the KnownZero/KnownOne bits to simplify things downstream.
   computeKnownBits(I, KnownZero, KnownOne, Depth, CxtI);
+
+  // If this user is only demanding bits that we know, return the known
+  // constant.
+  if ((DemandedMask & (KnownZero|KnownOne)) == DemandedMask)
+    return Constant::getIntegerValue(ITy, KnownOne);
+
   return nullptr;
 }
 


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