[PATCH] D47037: [ValueTracking][EarlyCSE][InstCombine] Improve EarlyCSE of some absolute value cases.

[Craig Topper via Phabricator via llvm-commits]

craig.topper updated this revision to Diff 147605.
craig.topper added a comment.

Remove the InstCombine change.


https://reviews.llvm.org/D47037

Files:
  lib/Analysis/ValueTracking.cpp
  lib/Transforms/Scalar/EarlyCSE.cpp
  test/Transforms/EarlyCSE/commute.ll


Index: test/Transforms/EarlyCSE/commute.ll
===================================================================
--- test/Transforms/EarlyCSE/commute.ll
+++ test/Transforms/EarlyCSE/commute.ll
@@ -252,3 +252,39 @@
   ret i8 %r
 }
 
+; These two tests make sure we still consider it a match when the RHS of the
+; compares are different.
+define i8 @abs_different_constants(i8 %a) {
+; CHECK-LABEL: @abs_different_constants(
+; CHECK-NEXT:    [[NEG:%.*]] = sub i8 0, %a
+; CHECK-NEXT:    [[CMP1:%.*]] = icmp sgt i8 %a, -1
+; CHECK-NEXT:    [[CMP2:%.*]] = icmp slt i8 %a, 0
+; CHECK-NEXT:    [[M1:%.*]] = select i1 [[CMP1]], i8 %a, i8 [[NEG]]
+; CHECK-NEXT:    ret i8 [[M1]]
+;
+  %neg = sub i8 0, %a
+  %cmp1 = icmp sgt i8 %a, -1
+  %cmp2 = icmp slt i8 %a, 0
+  %m1 = select i1 %cmp1, i8 %a, i8 %neg
+  %m2 = select i1 %cmp2, i8 %neg, i8 %a
+  %r = or i8 %m2, %m1
+  ret i8 %r
+}
+
+define i8 @nabs_different_constants(i8 %a) {
+; CHECK-LABEL: @nabs_different_constants(
+; CHECK-NEXT:    [[NEG:%.*]] = sub i8 0, %a
+; CHECK-NEXT:    [[CMP1:%.*]] = icmp slt i8 %a, 0
+; CHECK-NEXT:    [[CMP2:%.*]] = icmp sgt i8 %a, -1
+; CHECK-NEXT:    [[M1:%.*]] = select i1 [[CMP1]], i8 %a, i8 [[NEG]]
+; CHECK-NEXT:    ret i8 0
+;
+  %neg = sub i8 0, %a
+  %cmp1 = icmp slt i8 %a, 0
+  %cmp2 = icmp sgt i8 %a, -1
+  %m1 = select i1 %cmp1, i8 %a, i8 %neg
+  %m2 = select i1 %cmp2, i8 %neg, i8 %a
+  %r = xor i8 %m2, %m1
+  ret i8 %r
+}
+
Index: lib/Transforms/Scalar/EarlyCSE.cpp
===================================================================
--- lib/Transforms/Scalar/EarlyCSE.cpp
+++ lib/Transforms/Scalar/EarlyCSE.cpp
@@ -161,6 +161,10 @@
       std::swap(A, B);
     return hash_combine(Inst->getOpcode(), SPF, A, B);
   }
+  if (SPF == SPF_ABS || SPF == SPF_NABS) {
+    // ABS/NABS always puts the input in A and its negation in B.
+    return hash_combine(Inst->getOpcode(), SPF, A, B);
+  }
 
   if (CastInst *CI = dyn_cast<CastInst>(Inst))
     return hash_combine(CI->getOpcode(), CI->getType(), CI->getOperand(0));
@@ -230,8 +234,13 @@
       LSPF == SPF_ABS || LSPF == SPF_NABS) {
     Value *RHSA, *RHSB;
     SelectPatternFlavor RSPF = matchSelectPattern(RHSI, RHSA, RHSB).Flavor;
-    return (LSPF == RSPF && ((LHSA == RHSA && LHSB == RHSB) ||
-                             (LHSA == RHSB && LHSB == RHSA)));
+    if (LSPF == RSPF) {
+      // Abs results are placed in a defined order by matchSelectPattern.
+      if (LSPF == SPF_ABS || LSPF == SPF_NABS)
+        return LHSA == RHSA && LHSB == RHSB;
+      return ((LHSA == RHSA && LHSB == RHSB) ||
+              (LHSA == RHSB && LHSB == RHSA));
+    }
   }
 
   return false;
Index: lib/Analysis/ValueTracking.cpp
===================================================================
--- lib/Analysis/ValueTracking.cpp
+++ lib/Analysis/ValueTracking.cpp
@@ -4571,6 +4571,8 @@
   if (match(CmpRHS, m_APInt(C1))) {
     if ((CmpLHS == TrueVal && match(FalseVal, m_Neg(m_Specific(CmpLHS)))) ||
         (CmpLHS == FalseVal && match(TrueVal, m_Neg(m_Specific(CmpLHS))))) {
+      // Set RHS to the negate operand. LHS was assigned to CmpLHS earlier.
+      RHS = (CmpLHS == TrueVal) ? FalseVal : TrueVal;
 
       // ABS(X) ==> (X >s 0) ? X : -X and (X >s -1) ? X : -X
       // NABS(X) ==> (X >s 0) ? -X : X and (X >s -1) ? -X : X


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