[PATCH] D65336: [InstSimplify] remove quadratic time looping (PR42771)

[Sanjay Patel via Phabricator via llvm-commits]

spatel updated this revision to Diff 211982.
spatel marked an inline comment as done.
spatel added a comment.

Patch updated:
Don't bother trying to simplify an instruction if it has no uses (restores the previous logic).


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D65336/new/

https://reviews.llvm.org/D65336

Files:
  llvm/lib/Transforms/Scalar/InstSimplifyPass.cpp
  llvm/test/Transforms/InstSimplify/assume.ll


Index: llvm/test/Transforms/InstSimplify/assume.ll
===================================================================
--- llvm/test/Transforms/InstSimplify/assume.ll
+++ llvm/test/Transforms/InstSimplify/assume.ll
@@ -33,15 +33,15 @@
 }
 
 ; Similar to above: there's no way to know which assumption is truthful,
-; so just don't crash. The second icmp+assume gets processed later, so that
-; determines the return value.
+; so just don't crash.
 
 define i8 @conflicting_assumptions(i8 %x) !dbg !10 {
 ; CHECK-LABEL: @conflicting_assumptions(
+; CHECK-NEXT:    [[ADD:%.*]] = add i8 [[X:%.*]], 1, !dbg !10
 ; CHECK-NEXT:    call void @llvm.assume(i1 false)
-; CHECK-NEXT:    [[COND2:%.*]] = icmp eq i8 %x, 4
+; CHECK-NEXT:    [[COND2:%.*]] = icmp eq i8 [[X]], 4
 ; CHECK-NEXT:    call void @llvm.assume(i1 [[COND2]])
-; CHECK-NEXT:    ret i8 5
+; CHECK-NEXT:    ret i8 [[ADD]]
 ;
   %add = add i8 %x, 1, !dbg !11
   %cond1 = icmp eq i8 %x, 3
Index: llvm/lib/Transforms/Scalar/InstSimplifyPass.cpp
===================================================================
--- llvm/lib/Transforms/Scalar/InstSimplifyPass.cpp
+++ llvm/lib/Transforms/Scalar/InstSimplifyPass.cpp
@@ -33,37 +33,33 @@
   bool Changed = false;
 
   do {
-    for (BasicBlock *BB : depth_first(&F.getEntryBlock())) {
-      // Here be subtlety: the iterator must be incremented before the loop
-      // body (not sure why), so a range-for loop won't work here.
-      for (BasicBlock::iterator BI = BB->begin(), BE = BB->end(); BI != BE;) {
-        Instruction *I = &*BI++;
-        // The first time through the loop ToSimplify is empty and we try to
-        // simplify all instructions.  On later iterations ToSimplify is not
+    for (BasicBlock &BB : F) {
+      SmallVector<Instruction *, 8> DeadInstsInBB;
+      for (Instruction &I : BB) {
+        // The first time through the loop, ToSimplify is empty and we try to
+        // simplify all instructions. On later iterations, ToSimplify is not
         // empty and we only bother simplifying instructions that are in it.
-        if (!ToSimplify->empty() && !ToSimplify->count(I))
+        if (!ToSimplify->empty() && !ToSimplify->count(&I))
           continue;
 
-        // Don't waste time simplifying unused instructions.
-        if (!I->use_empty()) {
-          if (Value *V = SimplifyInstruction(I, SQ, ORE)) {
+        // Don't waste time simplifying dead/unused instructions.
+        if (isInstructionTriviallyDead(&I)) {
+          DeadInstsInBB.push_back(&I);
+        } else if (!I.use_empty()) {
+          if (Value *V = SimplifyInstruction(&I, SQ, ORE)) {
             // Mark all uses for resimplification next time round the loop.
-            for (User *U : I->users())
+            for (User *U : I.users())
               Next->insert(cast<Instruction>(U));
-            I->replaceAllUsesWith(V);
+            I.replaceAllUsesWith(V);
             ++NumSimplified;
             Changed = true;
+            // A call can get simplified, but it may not be trivially dead.
+            if (isInstructionTriviallyDead(&I))
+              DeadInstsInBB.push_back(&I);
           }
         }
-        if (RecursivelyDeleteTriviallyDeadInstructions(I, SQ.TLI)) {
-          // RecursivelyDeleteTriviallyDeadInstruction can remove more than one
-          // instruction, so simply incrementing the iterator does not work.
-          // When instructions get deleted re-iterate instead.
-          BI = BB->begin();
-          BE = BB->end();
-          Changed = true;
-        }
       }
+      RecursivelyDeleteTriviallyDeadInstructions(DeadInstsInBB, SQ.TLI);
     }
 
     // Place the list of instructions to simplify on the next loop iteration


-------------- next part --------------
A non-text attachment was scrubbed...
Name: D65336.211982.patch
Type: text/x-patch
Size: 3703 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20190726/ce44dcda/attachment.bin>