[llvm] b0f7876 - [SCCP] Propagate equality of a not-constant

[via llvm-commits]

Author: luxufan
Date: 2022-12-05T19:54:13+08:00
New Revision: b0f78769178ebb5e0691aca5143fead7f79ee55c

URL: https://github.com/llvm/llvm-project/commit/b0f78769178ebb5e0691aca5143fead7f79ee55c
DIFF: https://github.com/llvm/llvm-project/commit/b0f78769178ebb5e0691aca5143fead7f79ee55c.diff

LOG: [SCCP] Propagate equality of a not-constant

The equality state of a not-constant can be used to do constant
propagation. For example,
```
define i32 @equal_not_constant(ptr noundef %p, ptr noundef %q) {
entry:
  %cmp = icmp ne ptr %p, null
  br i1 %cmp, label %if.then, label %if.end

if.then:                                          ; preds = %entry
  %cmp.then = icmp eq ptr %p, %q
  br i1 %cmp.then, label %if.then1, label %if.end

if.then1:                                         ; preds = %if.then
  %cmp.then1 = icmp ne ptr %q, null
  call void @use(i1 %cmp.then1)
  br label %if.end

if.end:
  ret i32 0
}

```
In this case, we can fold `%cmp.then1` as `true`.

Reviewed By: nikic

Differential Revision: https://reviews.llvm.org/D139289

Added: 
    

Modified: 
    llvm/lib/Transforms/Utils/SCCPSolver.cpp
    llvm/test/Transforms/SCCP/conditions-ranges.ll

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Transforms/Utils/SCCPSolver.cpp b/llvm/lib/Transforms/Utils/SCCPSolver.cpp
index 4b779c58bbcf0..4bfec669dd103 100644
--- a/llvm/lib/Transforms/Utils/SCCPSolver.cpp
+++ b/llvm/lib/Transforms/Utils/SCCPSolver.cpp
@@ -1344,9 +1344,10 @@ void SCCPInstVisitor::handleCallResult(CallBase &CB) {
             IV, &CB,
             ValueLatticeElement::getRange(NewCR, /*MayIncludeUndef*/ false));
         return;
-      } else if (Pred == CmpInst::ICMP_EQ && CondVal.isConstant()) {
+      } else if (Pred == CmpInst::ICMP_EQ &&
+                 (CondVal.isConstant() || CondVal.isNotConstant())) {
         // For non-integer values or integer constant expressions, only
-        // propagate equal constants.
+        // propagate equal constants or not-constants.
         addAdditionalUser(OtherOp, &CB);
         mergeInValue(IV, &CB, CondVal);
         return;

diff  --git a/llvm/test/Transforms/SCCP/conditions-ranges.ll b/llvm/test/Transforms/SCCP/conditions-ranges.ll
index e108d63e9091f..3de2e9ca72a94 100644
--- a/llvm/test/Transforms/SCCP/conditions-ranges.ll
+++ b/llvm/test/Transforms/SCCP/conditions-ranges.ll
@@ -1370,6 +1370,69 @@ bb142:                                            ; preds = %bb139
   ret void
 }
 
+define i32 @equal_not_constant(ptr noundef %p, ptr noundef %q) {
+; CHECK-LABEL: @equal_not_constant(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[CMP:%.*]] = icmp ne ptr [[P:%.*]], null
+; CHECK-NEXT:    br i1 [[CMP]], label [[IF_THEN:%.*]], label [[IF_END:%.*]]
+; CHECK:       if.then:
+; CHECK-NEXT:    [[CMP_THEN:%.*]] = icmp eq ptr [[P]], [[Q:%.*]]
+; CHECK-NEXT:    br i1 [[CMP_THEN]], label [[IF_THEN1:%.*]], label [[IF_END]]
+; CHECK:       if.then1:
+; CHECK-NEXT:    call void @use(i1 true)
+; CHECK-NEXT:    br label [[IF_END]]
+; CHECK:       if.end:
+; CHECK-NEXT:    ret i32 0
+;
+entry:
+  %cmp = icmp ne ptr %p, null
+  br i1 %cmp, label %if.then, label %if.end
+
+if.then:                                          ; preds = %entry
+  %cmp.then = icmp eq ptr %p, %q
+  br i1 %cmp.then, label %if.then1, label %if.end
+
+if.then1:                                         ; preds = %if.then
+  %cmp.then1 = icmp ne ptr %q, null
+  call void @use(i1 %cmp.then1)
+  br label %if.end
+
+if.end:
+  ret i32 0
+}
+
+define i32 @not_equal_not_constant(ptr noundef %p, ptr noundef %q) {
+; CHECK-LABEL: @not_equal_not_constant(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[CMP:%.*]] = icmp ne ptr [[P:%.*]], null
+; CHECK-NEXT:    br i1 [[CMP]], label [[IF_THEN:%.*]], label [[IF_END:%.*]]
+; CHECK:       if.then:
+; CHECK-NEXT:    [[CMP_THEN:%.*]] = icmp ne ptr [[P]], [[Q:%.*]]
+; CHECK-NEXT:    br i1 [[CMP_THEN]], label [[IF_THEN1:%.*]], label [[IF_END]]
+; CHECK:       if.then1:
+; CHECK-NEXT:    [[CMP_THEN1:%.*]] = icmp ne ptr [[Q]], null
+; CHECK-NEXT:    call void @use(i1 [[CMP_THEN1]])
+; CHECK-NEXT:    br label [[IF_END]]
+; CHECK:       if.end:
+; CHECK-NEXT:    ret i32 0
+;
+entry:
+  %cmp = icmp ne ptr %p, null
+  br i1 %cmp, label %if.then, label %if.end
+
+if.then:                                          ; preds = %entry
+  %cmp.then = icmp ne ptr %p, %q
+  br i1 %cmp.then, label %if.then1, label %if.end
+
+if.then1:                                         ; preds = %if.then
+  %cmp.then1 = icmp ne ptr %q, null
+  call void @use(i1 %cmp.then1)
+  br label %if.end
+
+if.end:
+  ret i32 0
+}
+
 define i1 @ptr_icmp_data_layout() {
 ; CHECK-LABEL: @ptr_icmp_data_layout(
 ; CHECK-NEXT:    ret i1 false