[PATCH] D152499: [SCCP] Skip computing intrinsics if one of its args is unknownOrUndef

[luxufan via Phabricator via llvm-commits]

StephenFan created this revision.
StephenFan added reviewers: nikic, fhahn.
Herald added subscribers: hiraditya, kristof.beyls.
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For constant range supported intrinsics, we got consantrange from args
no matter if they are unknown or undef. And the constant range computed
from unknown or undef value state is full range.

I think compute with full constant range is harmful since although we
can do mergeIn after these args value state are changed, the merge
operation of two constant ranges is union.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D152499

Files:
  llvm/lib/Transforms/Utils/SCCPSolver.cpp
  llvm/test/Transforms/SCCP/intrinsics.ll


Index: llvm/test/Transforms/SCCP/intrinsics.ll
===================================================================
--- llvm/test/Transforms/SCCP/intrinsics.ll
+++ llvm/test/Transforms/SCCP/intrinsics.ll
@@ -10,7 +10,7 @@
 
 define void @abs1(ptr %p) {
 ; CHECK-LABEL: @abs1(
-; CHECK-NEXT:    [[X:%.*]] = load i8, ptr [[P:%.*]], align 1, [[RNG0:!range !.*]]
+; CHECK-NEXT:    [[X:%.*]] = load i8, ptr [[P:%.*]], align 1, !range [[RNG0:![0-9]+]]
 ; CHECK-NEXT:    [[ABS:%.*]] = call i8 @llvm.abs.i8(i8 [[X]], i1 false)
 ; CHECK-NEXT:    call void @use(i1 true)
 ; CHECK-NEXT:    call void @use(i1 true)
@@ -62,8 +62,8 @@
 
 define void @umax1(ptr %p1, ptr %p2) {
 ; CHECK-LABEL: @umax1(
-; CHECK-NEXT:    [[X1:%.*]] = load i8, ptr [[P1:%.*]], align 1, [[RNG1:!range !.*]]
-; CHECK-NEXT:    [[X2:%.*]] = load i8, ptr [[P2:%.*]], align 1, [[RNG2:!range !.*]]
+; CHECK-NEXT:    [[X1:%.*]] = load i8, ptr [[P1:%.*]], align 1, !range [[RNG1:![0-9]+]]
+; CHECK-NEXT:    [[X2:%.*]] = load i8, ptr [[P2:%.*]], align 1, !range [[RNG2:![0-9]+]]
 ; CHECK-NEXT:    [[M:%.*]] = call i8 @llvm.umax.i8(i8 [[X1]], i8 [[X2]])
 ; CHECK-NEXT:    call void @use(i1 true)
 ; CHECK-NEXT:    call void @use(i1 true)
@@ -98,3 +98,27 @@
   call void @use(i1 %cmp)
   ret void
 }
+
+define i8 @umax_including_undef(i1 %c.1, i1 %c.2) {
+; CHECK-LABEL: @umax_including_undef(
+; CHECK-NEXT:    br i1 [[C_1:%.*]], label [[TRUE:%.*]], label [[FALSE:%.*]]
+; CHECK:       true:
+; CHECK-NEXT:    br label [[EXIT:%.*]]
+; CHECK:       false:
+; CHECK-NEXT:    br label [[EXIT]]
+; CHECK:       exit:
+; CHECK-NEXT:    ret i8 3
+;
+  br i1 %c.1, label %true, label %false
+
+true:
+  br label %exit
+
+false:
+  br label %exit
+
+exit:
+  %p = phi i8 [ 3, %true], [ undef, %false ]
+  %p_umax = call i8 @llvm.umax.i8(i8 %p, i8 1)
+  ret i8 %p_umax
+}
Index: llvm/lib/Transforms/Utils/SCCPSolver.cpp
===================================================================
--- llvm/lib/Transforms/Utils/SCCPSolver.cpp
+++ llvm/lib/Transforms/Utils/SCCPSolver.cpp
@@ -1758,6 +1758,8 @@
       SmallVector<ConstantRange, 2> OpRanges;
       for (Value *Op : II->args()) {
         const ValueLatticeElement &State = getValueState(Op);
+        if (State.isUnknownOrUndef())
+          return;
         OpRanges.push_back(getConstantRange(State, Op->getType()));
       }
 


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