[ConstantFolding] Fix to prevent constant folding having to repeatedly scan operands. NFCI

After the loop unroll threshold was increased in r295538, very
large constant expressions can be created. This prevents them
from having to be recursively scanned, leading to a compile
time blow-up.

Differential Revision: https://reviews.llvm.org/D30689

llvm-svn: 298356

2 files changed, 74 insertions, 1 deletions

diff --git a/llvm/lib/Analysis/ConstantFolding.cpp b/llvm/lib/Analysis/ConstantFolding.cpp
index e6939c02238..c3ce648712b 100644
--- a/llvm/lib/Analysis/ConstantFolding.cpp
+++ b/llvm/lib/Analysis/ConstantFolding.cpp
@@ -1058,8 +1058,8 @@ ConstantFoldConstantImpl(const Constant *C, const DataLayout &DL,
       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});
         }
diff --git a/llvm/test/Analysis/ConstantFolding/timeout.ll b/llvm/test/Analysis/ConstantFolding/timeout.ll
new file mode 100644
index 00000000000..3d28c2adbe4
--- /dev/null
+++ b/llvm/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* }
+
+@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
+}
+