[llvm] 7796792 - Revert "[InstCombine] Remove early constant fold"

[Vitaly Buka via llvm-commits]

Author: Vitaly Buka
Date: 2023-02-24T10:21:32-08:00
New Revision: 779679284e99f70e741c303f14573b2b9cbea232

URL: https://github.com/llvm/llvm-project/commit/779679284e99f70e741c303f14573b2b9cbea232
DIFF: https://github.com/llvm/llvm-project/commit/779679284e99f70e741c303f14573b2b9cbea232.diff

LOG: Revert "[InstCombine] Remove early constant fold"

Increase compile time with ubsan ARM from 3 to 14 min single file.
I upload reproducer into D144369.

Also we have random timeouts on internal x86_64 builds.
Both bisected to this one.

This reverts commit 45a0b812fa13ec255cae91f974540a4d805a8d79.

Added: 
    

Modified: 
    llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
    llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
    llvm/test/Transforms/InstCombine/pr38677.ll

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
index 7e5354047ebc6..0b3f92d5c5275 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
@@ -308,10 +308,6 @@ Instruction *InstCombinerImpl::commonCastTransforms(CastInst &CI) {
   Value *Src = CI.getOperand(0);
   Type *Ty = CI.getType();
 
-  if (auto *SrcC = dyn_cast<Constant>(Src))
-    if (Constant *Res = ConstantFoldCastOperand(CI.getOpcode(), SrcC, Ty, DL))
-      return replaceInstUsesWith(CI, Res);
-
   // Try to eliminate a cast of a cast.
   if (auto *CSrc = dyn_cast<CastInst>(Src)) {   // A->B->C cast
     if (Instruction::CastOps NewOpc = isEliminableCastPair(CSrc, &CI)) {

diff  --git a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
index 34d1b2b46db29..3366eaec235fa 100644
--- a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
@@ -4238,6 +4238,23 @@ bool InstCombinerImpl::run() {
     if (!DebugCounter::shouldExecute(VisitCounter))
       continue;
 
+    // Instruction isn't dead, see if we can constant propagate it.
+    if (!I->use_empty() &&
+        (I->getNumOperands() == 0 || isa<Constant>(I->getOperand(0)))) {
+      if (Constant *C = ConstantFoldInstruction(I, DL, &TLI)) {
+        LLVM_DEBUG(dbgs() << "IC: ConstFold to: " << *C << " from: " << *I
+                          << '\n');
+
+        // Add operands to the worklist.
+        replaceInstUsesWith(*I, C);
+        ++NumConstProp;
+        if (isInstructionTriviallyDead(I, &TLI))
+          eraseInstFromFunction(*I);
+        MadeIRChange = true;
+        continue;
+      }
+    }
+
     // See if we can trivially sink this instruction to its user if we can
     // prove that the successor is not executed more frequently than our block.
     // Return the UserBlock if successful.

diff  --git a/llvm/test/Transforms/InstCombine/pr38677.ll b/llvm/test/Transforms/InstCombine/pr38677.ll
index f60c7fb209f21..bacee2c676768 100644
--- a/llvm/test/Transforms/InstCombine/pr38677.ll
+++ b/llvm/test/Transforms/InstCombine/pr38677.ll
@@ -11,8 +11,9 @@ define i32 @foo(i1 %which, ptr %dst) {
 ; CHECK:       delay:
 ; CHECK-NEXT:    br label [[FINAL]]
 ; CHECK:       final:
+; CHECK-NEXT:    [[USE2:%.*]] = phi i32 [ 1, [[ENTRY:%.*]] ], [ select (i1 icmp eq (ptr @A, ptr @B), i32 2, i32 1), [[DELAY]] ]
 ; CHECK-NEXT:    store i1 false, ptr [[DST:%.*]], align 1
-; CHECK-NEXT:    ret i32 1
+; CHECK-NEXT:    ret i32 [[USE2]]
 ;
 entry:
   br i1 true, label %final, label %delay