[llvm] 9b99459 - [SCCP] Only handle unknown lattice values in resolvedUndefsIn()

[Nikita Popov via llvm-commits]

Author: Nikita Popov
Date: 2022-07-01T09:14:37+02:00
New Revision: 9b994593cc2aec4c4979400ec747965bd3823bc0

URL: https://github.com/llvm/llvm-project/commit/9b994593cc2aec4c4979400ec747965bd3823bc0
DIFF: https://github.com/llvm/llvm-project/commit/9b994593cc2aec4c4979400ec747965bd3823bc0.diff

LOG: [SCCP] Only handle unknown lattice values in resolvedUndefsIn()

This is a minor refinement of resolvedUndefsIn(), mostly for clarity.
If the value of an instruction is undef, then that's already a legal
final result -- we can safely rauw such an instruction with undef.
We only need to mark unknown values as overdefined, as that's the
result we get for an instruction that has not been processed because
it has an undef operand.

Differential Revision: https://reviews.llvm.org/D128251

Added: 
    

Modified: 
    llvm/lib/Transforms/Utils/SCCPSolver.cpp
    llvm/test/Transforms/SCCP/PR26044.ll
    llvm/test/Transforms/SCCP/ipsccp-phi-one-pred-dead.ll

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Transforms/Utils/SCCPSolver.cpp b/llvm/lib/Transforms/Utils/SCCPSolver.cpp
index 9858471cb09fe..eee91e70292e3 100644
--- a/llvm/lib/Transforms/Utils/SCCPSolver.cpp
+++ b/llvm/lib/Transforms/Utils/SCCPSolver.cpp
@@ -1456,7 +1456,7 @@ void SCCPInstVisitor::solve() {
 /// However, if the operand remains undef when the solver returns, we do need
 /// to assign some result to the instruction (otherwise we would treat it as
 /// unreachable). For simplicity, we mark any instructions that are still
-/// unknown/undef as overdefined.
+/// unknown as overdefined.
 bool SCCPInstVisitor::resolvedUndefsIn(Function &F) {
   bool MadeChange = false;
   for (BasicBlock &BB : F) {
@@ -1485,7 +1485,7 @@ bool SCCPInstVisitor::resolvedUndefsIn(Function &F) {
         // more precise than this but it isn't worth bothering.
         for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) {
           ValueLatticeElement &LV = getStructValueState(&I, i);
-          if (LV.isUnknownOrUndef()) {
+          if (LV.isUnknown()) {
             markOverdefined(LV, &I);
             MadeChange = true;
           }
@@ -1494,7 +1494,7 @@ bool SCCPInstVisitor::resolvedUndefsIn(Function &F) {
       }
 
       ValueLatticeElement &LV = getValueState(&I);
-      if (!LV.isUnknownOrUndef())
+      if (!LV.isUnknown())
         continue;
 
       // There are two reasons a call can have an undef result

diff  --git a/llvm/test/Transforms/SCCP/PR26044.ll b/llvm/test/Transforms/SCCP/PR26044.ll
index a5a5c4d8c0bda..2a8ac7c3971ae 100644
--- a/llvm/test/Transforms/SCCP/PR26044.ll
+++ b/llvm/test/Transforms/SCCP/PR26044.ll
@@ -11,8 +11,7 @@ define void @fn2(i32* %P) {
 ; CHECK:       for.cond1:
 ; CHECK-NEXT:    unreachable
 ; CHECK:       if.end:
-; CHECK-NEXT:    [[TMP0:%.*]] = load i32, i32* undef, align 4
-; CHECK-NEXT:    [[CALL:%.*]] = call i32 @fn1(i32 [[TMP0]])
+; CHECK-NEXT:    [[CALL:%.*]] = call i32 @fn1(i32 undef)
 ; CHECK-NEXT:    store i32 [[CALL]], i32* [[P]], align 4
 ; CHECK-NEXT:    br label [[FOR_COND1:%.*]]
 ;
@@ -34,8 +33,8 @@ define internal i32 @fn1(i32 %p1) {
 ; CHECK-LABEL: define {{[^@]+}}@fn1
 ; CHECK-SAME: (i32 [[P1:%.*]]) {
 ; CHECK-NEXT:  entry:
-; CHECK-NEXT:    [[TOBOOL:%.*]] = icmp ne i32 [[P1]], 0
-; CHECK-NEXT:    [[COND:%.*]] = select i1 [[TOBOOL]], i32 [[P1]], i32 [[P1]]
+; CHECK-NEXT:    [[TOBOOL:%.*]] = icmp ne i32 undef, 0
+; CHECK-NEXT:    [[COND:%.*]] = select i1 [[TOBOOL]], i32 undef, i32 undef
 ; CHECK-NEXT:    ret i32 [[COND]]
 ;
 entry:
@@ -52,8 +51,7 @@ define void @fn_no_null_opt(i32* %P) #0 {
 ; CHECK:       for.cond1:
 ; CHECK-NEXT:    unreachable
 ; CHECK:       if.end:
-; CHECK-NEXT:    [[TMP0:%.*]] = load i32, i32* undef, align 4
-; CHECK-NEXT:    [[CALL:%.*]] = call i32 @fn0(i32 [[TMP0]])
+; CHECK-NEXT:    [[CALL:%.*]] = call i32 @fn0(i32 undef)
 ; CHECK-NEXT:    store i32 [[CALL]], i32* [[P]], align 4
 ; CHECK-NEXT:    br label [[FOR_COND1:%.*]]
 ;
@@ -75,8 +73,8 @@ define internal i32 @fn0(i32 %p1) {
 ; CHECK-LABEL: define {{[^@]+}}@fn0
 ; CHECK-SAME: (i32 [[P1:%.*]]) {
 ; CHECK-NEXT:  entry:
-; CHECK-NEXT:    [[TOBOOL:%.*]] = icmp ne i32 [[P1]], 0
-; CHECK-NEXT:    [[COND:%.*]] = select i1 [[TOBOOL]], i32 [[P1]], i32 [[P1]]
+; CHECK-NEXT:    [[TOBOOL:%.*]] = icmp ne i32 undef, 0
+; CHECK-NEXT:    [[COND:%.*]] = select i1 [[TOBOOL]], i32 undef, i32 undef
 ; CHECK-NEXT:    ret i32 [[COND]]
 ;
 entry:

diff  --git a/llvm/test/Transforms/SCCP/ipsccp-phi-one-pred-dead.ll b/llvm/test/Transforms/SCCP/ipsccp-phi-one-pred-dead.ll
index 9e718a0638b94..34bb1b650ab50 100644
--- a/llvm/test/Transforms/SCCP/ipsccp-phi-one-pred-dead.ll
+++ b/llvm/test/Transforms/SCCP/ipsccp-phi-one-pred-dead.ll
@@ -5,17 +5,13 @@ target triple = "x86_64-unknown-linux-gnu"
 define void @test() {
 ; CHECK-LABEL: @test(
 ; CHECK-NEXT:  entry:
-; CHECK-NEXT:    br label %Flow5.pre
+; CHECK-NEXT:    br label [[FLOW5_PRE:%.*]]
 ; CHECK:       Flow6:
-; CHECK-NEXT:    br i1 undef, label %end1, label %end2
+; CHECK-NEXT:    unreachable
 ; CHECK:       Flow5.pre:
-; CHECK-NEXT:    br label %Flow5
+; CHECK-NEXT:    br label [[FLOW5:%.*]]
 ; CHECK:       Flow5:
-; CHECK-NEXT:    br label %Flow6
-; CHECK:       end1:
-; CHECK-NEXT:    unreachable
-; CHECK:       end2:
-; CHECK-NEXT:    unreachable
+; CHECK-NEXT:    br label [[FLOW6:%.*]]
 ;
 entry:
   br i1 true, label %Flow5.pre, label %Flow5.pre.unreachable