[PATCH] D30689: [ConstantFolding] Small fix to prevent constant folding having to repeatedly scan operands.

[Dave Green via Phabricator via llvm-commits]

dmgreen updated this revision to Diff 91759.
dmgreen added a comment.

Hello,

Thanks for taking a look. The only test I could come up with would be one that times out given a high enough LOOP define in the above reproducer. This patch should otherwise be an NFC.

I don't see any other examples of tests we have that are expected to not timeout, but I've come up with something that should, with the patch, compile fine. I'm not sure if it's a great test (without the fix it will just hang) but at least it's something.

Dave


https://reviews.llvm.org/D30689

Files:
  lib/Analysis/ConstantFolding.cpp
  test/Analysis/ConstantFolding/timeout.ll


Index: test/Analysis/ConstantFolding/timeout.ll
===================================================================
--- /dev/null
+++ test/Analysis/ConstantFolding/timeout.ll
@@ -0,0 +1,73 @@
+; NOTE: This is a timeout test for some O(something silly) constant folding behaviour. It may not be the best test. Providing it finishes, it passes.
+; RUN: opt < %s -O3 -S | FileCheck %s
+target datalayout = "e-m:e-p:32:32-i64:64-v128:64:128-a:0:32-n32-S64"
+target triple = "armv8-none-eabi"
+
+%struct.ST = type { %struct.ST* }
+
+ at global = internal global [121 x i8] zeroinitializer, align 1
+
+define void @func() #0 {
+;CHECK-LABEL: func
+entry:
+  %s = alloca %struct.ST*, align 4
+  %j = alloca i32, align 4
+  store %struct.ST* bitcast ([121 x i8]* @global to %struct.ST*), %struct.ST** %s, align 4
+  store i32 0, i32* %j, align 4
+  br label %for.cond
+
+for.cond:                                         ; preds = %for.inc, %entry
+  %0 = load i32, i32* %j, align 4
+  %cmp = icmp slt i32 %0, 30
+  br i1 %cmp, label %for.body, label %for.end
+
+for.body:                                         ; preds = %for.cond
+  %1 = load %struct.ST*, %struct.ST** %s, align 4
+  %2 = bitcast %struct.ST* %1 to i8*
+  %add.ptr = getelementptr inbounds i8, i8* %2, i32 4
+  %3 = ptrtoint i8* %add.ptr to i32
+  %4 = load %struct.ST*, %struct.ST** %s, align 4
+  %5 = bitcast %struct.ST* %4 to i8*
+  %add.ptr1 = getelementptr inbounds i8, i8* %5, i32 4
+  %6 = ptrtoint i8* %add.ptr1 to i32
+  %rem = urem i32 %6, 2
+  %cmp2 = icmp eq i32 %rem, 0
+  br i1 %cmp2, label %cond.true, label %cond.false
+
+cond.true:                                        ; preds = %for.body
+  br label %cond.end
+
+cond.false:                                       ; preds = %for.body
+  %7 = load %struct.ST*, %struct.ST** %s, align 4
+  %8 = bitcast %struct.ST* %7 to i8*
+  %add.ptr3 = getelementptr inbounds i8, i8* %8, i32 4
+  %9 = ptrtoint i8* %add.ptr3 to i32
+  %rem4 = urem i32 %9, 2
+  br label %cond.end
+
+cond.end:                                         ; preds = %cond.false, %cond.true
+  %cond = phi i32 [ 0, %cond.true ], [ %rem4, %cond.false ]
+  %add = add i32 %3, %cond
+  %10 = inttoptr i32 %add to %struct.ST*
+  %11 = load %struct.ST*, %struct.ST** %s, align 4
+  %next = getelementptr inbounds %struct.ST, %struct.ST* %11, i32 0, i32 0
+  store %struct.ST* %10, %struct.ST** %next, align 4
+  %12 = load %struct.ST*, %struct.ST** %s, align 4
+  %next5 = getelementptr inbounds %struct.ST, %struct.ST* %12, i32 0, i32 0
+  %13 = load %struct.ST*, %struct.ST** %next5, align 4
+  store %struct.ST* %13, %struct.ST** %s, align 4
+  br label %for.inc
+
+for.inc:                                          ; preds = %cond.end
+  %14 = load i32, i32* %j, align 4
+  %inc = add nsw i32 %14, 1
+  store i32 %inc, i32* %j, align 4
+  br label %for.cond
+
+for.end:                                          ; preds = %for.cond
+  %15 = load %struct.ST*, %struct.ST** %s, align 4
+  %next6 = getelementptr inbounds %struct.ST, %struct.ST* %15, i32 0, i32 0
+  store %struct.ST* null, %struct.ST** %next6, align 4
+  ret void
+}
+
Index: lib/Analysis/ConstantFolding.cpp
===================================================================
--- lib/Analysis/ConstantFolding.cpp
+++ lib/Analysis/ConstantFolding.cpp
@@ -1058,8 +1058,8 @@
       if (It == FoldedOps.end()) {
         if (auto *FoldedC =
                 ConstantFoldConstantImpl(NewC, DL, TLI, FoldedOps)) {
-          NewC = FoldedC;
           FoldedOps.insert({NewC, FoldedC});
+          NewC = FoldedC;
         } else {
           FoldedOps.insert({NewC, NewC});
         }


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