[PATCH] D53036: [InstCombine] Demand bits of UMin

[Dave Green via Phabricator via llvm-commits]

This revision was automatically updated to reflect the committed changes.
Closed by commit rL344239: [InstCombine] Demand bits of UMin (authored by dmgreen, committed by ).

Changed prior to commit:
  https://reviews.llvm.org/D53036?vs=169002&id=169190#toc

Repository:
  rL LLVM

https://reviews.llvm.org/D53036

Files:
  llvm/trunk/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
  llvm/trunk/test/Transforms/InstCombine/minmax-demandbits.ll


Index: llvm/trunk/test/Transforms/InstCombine/minmax-demandbits.ll
===================================================================
--- llvm/trunk/test/Transforms/InstCombine/minmax-demandbits.ll
+++ llvm/trunk/test/Transforms/InstCombine/minmax-demandbits.ll
@@ -190,9 +190,7 @@
 
 define i8 @or_min_31_30(i8 %A) {
 ; CHECK-LABEL: @or_min_31_30(
-; CHECK-NEXT:    [[CMP:%.*]] = icmp ult i8 [[A:%.*]], -30
-; CHECK-NEXT:    [[MIN:%.*]] = select i1 [[CMP]], i8 [[A]], i8 -30
-; CHECK-NEXT:    [[R:%.*]] = or i8 [[MIN]], 31
+; CHECK-NEXT:    [[R:%.*]] = or i8 [[A:%.*]], 31
 ; CHECK-NEXT:    ret i8 [[R]]
 ;
   %cmp = icmp ult i8 %A, -30
@@ -203,9 +201,7 @@
 
 define i8 @and_min_7_7(i8 %A) {
 ; CHECK-LABEL: @and_min_7_7(
-; CHECK-NEXT:    [[L2:%.*]] = icmp ult i8 [[A:%.*]], -7
-; CHECK-NEXT:    [[MIN:%.*]] = select i1 [[L2]], i8 [[A]], i8 -7
-; CHECK-NEXT:    [[R:%.*]] = and i8 [[MIN]], -8
+; CHECK-NEXT:    [[R:%.*]] = and i8 [[A:%.*]], -8
 ; CHECK-NEXT:    ret i8 [[R]]
 ;
   %l2 = icmp ult i8 %A, -7
@@ -216,9 +212,7 @@
 
 define i8 @and_min_7_8(i8 %A) {
 ; CHECK-LABEL: @and_min_7_8(
-; CHECK-NEXT:    [[L2:%.*]] = icmp ult i8 [[A:%.*]], -8
-; CHECK-NEXT:    [[MIN:%.*]] = select i1 [[L2]], i8 [[A]], i8 -8
-; CHECK-NEXT:    [[R:%.*]] = and i8 [[MIN]], -8
+; CHECK-NEXT:    [[R:%.*]] = and i8 [[A:%.*]], -8
 ; CHECK-NEXT:    ret i8 [[R]]
 ;
   %l2 = icmp ult i8 %A, -8
Index: llvm/trunk/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
===================================================================
--- llvm/trunk/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
+++ llvm/trunk/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
@@ -325,6 +325,16 @@
       unsigned CTZ = DemandedMask.countTrailingZeros();
       if (match(RHS, m_APInt(C)) && CTZ >= C->getActiveBits())
         return LHS;
+    } else if (SPF == SPF_UMIN) {
+      // UMin(A, C) == A if ...
+      // The lowest non-zero bit of DemandMask is higher than the highest
+      // non-one bit of C.
+      // This comes from using DeMorgans on the above umax example.
+      const APInt *C;
+      unsigned CTZ = DemandedMask.countTrailingZeros();
+      if (match(RHS, m_APInt(C)) &&
+          CTZ >= C->getBitWidth() - C->countLeadingOnes())
+        return LHS;
     }
 
     // If this is a select as part of any other min/max pattern, don't simplify


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