From: Sanjay Patel <spatel@rotateright.com>
Date: Tue, 19 Feb 2019 21:46:13 +0000 (+0000)
Subject: [InstCombine] rearrange saturated add folds; NFC
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=783c1f039fbc684ef40cbb9996eca453e94bfd02;p=llvm

[InstCombine] rearrange saturated add folds; NFC

This is no-functional-change-intended, but that was also
true when it was part of rL354276, and I managed to lose
2 predicates for the fold with constant...causing much bot
distress. So this time I'm adding a couple of negative tests
to avoid that.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@354384 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/lib/Transforms/InstCombine/InstCombineSelect.cpp b/lib/Transforms/InstCombine/InstCombineSelect.cpp
index 3ee418feb0e..0e9d6f05275 100644
--- a/lib/Transforms/InstCombine/InstCombineSelect.cpp
+++ b/lib/Transforms/InstCombine/InstCombineSelect.cpp
@@ -680,10 +680,22 @@ static Value *canonicalizeSaturatedAdd(ICmpInst *Cmp, Value *TVal, Value *FVal,
   if (!Cmp->hasOneUse())
     return nullptr;
 
-  // Canonicalize to 'ULT' to simplify matching below.
+  // Match unsigned saturated add with constant.
   Value *Cmp0 = Cmp->getOperand(0);
   Value *Cmp1 = Cmp->getOperand(1);
   ICmpInst::Predicate Pred = Cmp->getPredicate();
+  Value *X;
+  const APInt *C, *CmpC;
+  if (Pred == ICmpInst::ICMP_ULT &&
+      match(TVal, m_Add(m_Value(X), m_APInt(C))) && X == Cmp0 &&
+      match(FVal, m_AllOnes()) && match(Cmp1, m_APInt(CmpC)) && *CmpC == ~*C) {
+    // Commute compare predicate and select operands:
+    // (X u< ~C) ? (X + C) : -1 --> (X u> ~C) ? -1 : (X + C)
+    Value *NewCmp = Builder.CreateICmp(ICmpInst::ICMP_UGT, X, Cmp1);
+    return Builder.CreateSelect(NewCmp, FVal, TVal);
+  }
+
+  // Canonicalize to 'ULT' to simplify matching below.
   if (Pred == ICmpInst::ICMP_UGT) {
     Pred = ICmpInst::ICMP_ULT;
     std::swap(Cmp0, Cmp1);
@@ -694,7 +706,7 @@ static Value *canonicalizeSaturatedAdd(ICmpInst *Cmp, Value *TVal, Value *FVal,
 
   // Match unsigned saturated add of 2 variables with an unnecessary 'not'.
   // TODO: There are more variations of this pattern.
-  Value *X, *Y;
+  Value *Y;
   if (match(TVal, m_AllOnes()) && match(Cmp0, m_Not(m_Value(X))) &&
       match(FVal, m_c_Add(m_Specific(X), m_Value(Y))) && Y == Cmp1) {
     // Change the comparison to use the sum (false value of the select). That is
@@ -706,16 +718,6 @@ static Value *canonicalizeSaturatedAdd(ICmpInst *Cmp, Value *TVal, Value *FVal,
     return Builder.CreateSelect(NewCmp, TVal, FVal);
   }
 
-  // Match unsigned saturated add with constant.
-  const APInt *C, *CmpC;
-  if (match(TVal, m_Add(m_Value(X), m_APInt(C))) && X == Cmp0 &&
-      match(FVal, m_AllOnes()) && match(Cmp1, m_APInt(CmpC)) && *CmpC == ~*C) {
-    // Commute compare predicate and select operands:
-    // (X u< ~C) ? (X + C) : -1 --> (X u> ~C) ? -1 : (X + C)
-    Value *NewCmp = Builder.CreateICmp(ICmpInst::ICMP_UGT, X, Cmp1);
-    return Builder.CreateSelect(NewCmp, FVal, TVal);
-  }
-
   return nullptr;
 }
 
diff --git a/test/Transforms/InstCombine/saturating-add-sub.ll b/test/Transforms/InstCombine/saturating-add-sub.ll
index de3af0008c9..da3daecf393 100644
--- a/test/Transforms/InstCombine/saturating-add-sub.ll
+++ b/test/Transforms/InstCombine/saturating-add-sub.ll
@@ -771,6 +771,36 @@ define i32 @uadd_sat_commute_select_ugt_commute_add(i32 %xp, i32 %y) {
   ret i32 %r
 }
 
+; Negative test - make sure we have a -1 in the select.
+
+define i32 @not_uadd_sat(i32 %x, i32 %y) {
+; CHECK-LABEL: @not_uadd_sat(
+; CHECK-NEXT:    [[A:%.*]] = add i32 [[X:%.*]], -2
+; CHECK-NEXT:    [[C:%.*]] = icmp ugt i32 [[X]], 1
+; CHECK-NEXT:    [[R:%.*]] = select i1 [[C]], i32 [[A]], i32 [[Y:%.*]]
+; CHECK-NEXT:    ret i32 [[R]]
+;
+  %a = add i32 %x, -2
+  %c = icmp ugt i32 %x, 1
+  %r = select i1 %c, i32 %a, i32 %y
+  ret i32 %r
+}
+
+; Negative test - make sure the predicate is 'ult'.
+
+define i32 @not_uadd_sat2(i32 %x, i32 %y) {
+; CHECK-LABEL: @not_uadd_sat2(
+; CHECK-NEXT:    [[A:%.*]] = add i32 [[X:%.*]], -2
+; CHECK-NEXT:    [[C:%.*]] = icmp ugt i32 [[X]], 1
+; CHECK-NEXT:    [[R:%.*]] = select i1 [[C]], i32 [[A]], i32 -1
+; CHECK-NEXT:    ret i32 [[R]]
+;
+  %a = add i32 %x, -2
+  %c = icmp ugt i32 %x, 1
+  %r = select i1 %c, i32 %a, i32 -1
+  ret i32 %r
+}
+
 define i32 @uadd_sat_constant(i32 %x) {
 ; CHECK-LABEL: @uadd_sat_constant(
 ; CHECK-NEXT:    [[A:%.*]] = add i32 [[X:%.*]], 42