[PATCH] D62703: [CVP] Simplify non-overflowing saturating add/sub

[Nikita Popov via Phabricator via llvm-commits]

nikic created this revision.
nikic added reviewers: spatel, lebedev.ri, reames.
Herald added subscribers: llvm-commits, hiraditya.
Herald added a project: LLVM.

If we can determine that a saturating add/sub will not overflow based on range analysis, convert it into a simple binary operation. This is a sibling transform to the existing with.overflow handling.


Repository:
  rL LLVM

https://reviews.llvm.org/D62703

Files:
  llvm/lib/Transforms/Scalar/CorrelatedValuePropagation.cpp
  llvm/test/Transforms/CorrelatedValuePropagation/overflows.ll


Index: llvm/test/Transforms/CorrelatedValuePropagation/overflows.ll
===================================================================
--- llvm/test/Transforms/CorrelatedValuePropagation/overflows.ll
+++ llvm/test/Transforms/CorrelatedValuePropagation/overflows.ll
@@ -739,8 +739,8 @@
 ; CHECK-NEXT:    call void @llvm.trap()
 ; CHECK-NEXT:    unreachable
 ; CHECK:       cont:
-; CHECK-NEXT:    [[RES:%.*]] = call i8 @llvm.uadd.sat.i8(i8 [[X]], i8 100)
-; CHECK-NEXT:    ret i8 [[RES]]
+; CHECK-NEXT:    [[RES1:%.*]] = add nuw i8 [[X]], 100
+; CHECK-NEXT:    ret i8 [[RES1]]
 ;
   %cmp = icmp ugt i8 %x, 100
   br i1 %cmp, label %trap, label %cont
@@ -762,8 +762,8 @@
 ; CHECK-NEXT:    call void @llvm.trap()
 ; CHECK-NEXT:    unreachable
 ; CHECK:       cont:
-; CHECK-NEXT:    [[RES:%.*]] = call i8 @llvm.sadd.sat.i8(i8 [[X]], i8 20)
-; CHECK-NEXT:    ret i8 [[RES]]
+; CHECK-NEXT:    [[RES1:%.*]] = add nsw i8 [[X]], 20
+; CHECK-NEXT:    ret i8 [[RES1]]
 ;
   %cmp = icmp sgt i8 %x, 100
   br i1 %cmp, label %trap, label %cont
@@ -785,8 +785,8 @@
 ; CHECK-NEXT:    call void @llvm.trap()
 ; CHECK-NEXT:    unreachable
 ; CHECK:       cont:
-; CHECK-NEXT:    [[RES:%.*]] = call i8 @llvm.usub.sat.i8(i8 [[X]], i8 100)
-; CHECK-NEXT:    ret i8 [[RES]]
+; CHECK-NEXT:    [[RES1:%.*]] = sub nuw i8 [[X]], 100
+; CHECK-NEXT:    ret i8 [[RES1]]
 ;
   %cmp = icmp ult i8 %x, 100
   br i1 %cmp, label %trap, label %cont
@@ -808,8 +808,8 @@
 ; CHECK-NEXT:    call void @llvm.trap()
 ; CHECK-NEXT:    unreachable
 ; CHECK:       cont:
-; CHECK-NEXT:    [[RES:%.*]] = call i8 @llvm.ssub.sat.i8(i8 [[X]], i8 20)
-; CHECK-NEXT:    ret i8 [[RES]]
+; CHECK-NEXT:    [[RES1:%.*]] = sub nsw i8 [[X]], 20
+; CHECK-NEXT:    ret i8 [[RES1]]
 ;
   %cmp = icmp slt i8 %x, -100
   br i1 %cmp, label %trap, label %cont
Index: llvm/lib/Transforms/Scalar/CorrelatedValuePropagation.cpp
===================================================================
--- llvm/lib/Transforms/Scalar/CorrelatedValuePropagation.cpp
+++ llvm/lib/Transforms/Scalar/CorrelatedValuePropagation.cpp
@@ -428,6 +428,20 @@
   ++NumOverflows;
 }
 
+static void processSaturatingInst(SaturatingInst *SI) {
+  BinaryOperator *BinOp = BinaryOperator::Create(
+      SI->getBinaryOp(), SI->getLHS(), SI->getRHS(), SI->getName(), SI);
+  BinOp->setDebugLoc(SI->getDebugLoc());
+  if (SI->isSigned())
+    BinOp->setHasNoSignedWrap();
+  else
+    BinOp->setHasNoUnsignedWrap();
+
+  SI->replaceAllUsesWith(BinOp);
+  SI->eraseFromParent();
+  ++NumOverflows;
+}
+
 /// Infer nonnull attributes for the arguments at the specified callsite.
 static bool processCallSite(CallSite CS, LazyValueInfo *LVI) {
   SmallVector<unsigned, 4> ArgNos;
@@ -440,6 +454,13 @@
     }
   }
 
+  if (auto *SI = dyn_cast<SaturatingInst>(CS.getInstruction())) {
+    if (willNotOverflow(SI, LVI)) {
+      processSaturatingInst(SI);
+      return true;
+    }
+  }
+
   // Deopt bundle operands are intended to capture state with minimal
   // perturbance of the code otherwise.  If we can find a constant value for
   // any such operand and remove a use of the original value, that's


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