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[LoopIdiom] BCmp: loop exit count must not be wider than size_t that bcmp
takes
As reported by Joerg Sonnenberger in IRC, for 32-bit systems, where pointer and size_t are 32-bit, if you use 64-bit-wide variable in the loop, you could end up with loop exit count being of the type wider than the size_t. Now, i'm not sure if we can produce `bcmp` from that (just truncate?), but we certainly should not assert/miscompile. llvm-svn: 374811
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@ -2080,6 +2080,10 @@ bool LoopIdiomRecognize::recognizeBCmpLoopSCEV(uint64_t BCmpTyBytes,
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LLVM_DEBUG(dbgs() << "SCEV expressions for loads are acceptable.\n");
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// bcmp / memcmp take length argument as size_t, so let's conservatively
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// assume that the iteration count should be not wider than that.
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Type *CmpFuncSizeTy = DL->getIntPtrType(SE->getContext());
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// For how many iterations is loop guaranteed not to exit via LoopLatch?
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// This is one less than the maximal number of comparisons,and is: n + -1
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const SCEV *LoopExitCount =
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@ -2089,6 +2093,8 @@ bool LoopIdiomRecognize::recognizeBCmpLoopSCEV(uint64_t BCmpTyBytes,
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// Exit count, similarly, must be loop-invant that dominates the loop header.
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if (LoopExitCount == SE->getCouldNotCompute() ||
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!LoopExitCount->getType()->isIntOrPtrTy() ||
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LoopExitCount->getType()->getScalarSizeInBits() >
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CmpFuncSizeTy->getScalarSizeInBits() ||
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!SE->isAvailableAtLoopEntry(LoopExitCount, CurLoop)) {
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LLVM_DEBUG(dbgs() << "Unsupported SCEV expression for loop latch exit.\n");
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return false;
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@ -1758,3 +1758,62 @@ cleanup:
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%res = phi i1 [ false, %for.body ], [ true, %for.cond ], [ false, %entry ]
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ret i1 %res
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}
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; With -m32:
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; int index_wider_than_pointer(int* a, int* b, long long num) {
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; for(long long i = 0; i < num; ++i) {
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; if(a[i] != b[i])
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; return 1;
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; }
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; return 0;
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; }
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define dso_local i64 @test(i64* %a, i64* %b, i128 %num) {
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; CHECK-LABEL: @test(
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; CHECK-NEXT: entry:
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; CHECK-NEXT: [[CMP9:%.*]] = icmp sgt i128 [[NUM:%.*]], 0
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; CHECK-NEXT: br i1 [[CMP9]], label [[FOR_BODY_PREHEADER:%.*]], label [[CLEANUP:%.*]]
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; CHECK: for.body.preheader:
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; CHECK-NEXT: br label [[FOR_BODY:%.*]]
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; CHECK: for.cond:
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; CHECK-NEXT: [[CMP:%.*]] = icmp slt i128 [[INC:%.*]], [[NUM]]
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; CHECK-NEXT: br i1 [[CMP]], label [[FOR_BODY]], label [[CLEANUP_LOOPEXIT:%.*]]
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; CHECK: for.body:
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; CHECK-NEXT: [[I_010:%.*]] = phi i128 [ [[INC]], [[FOR_COND:%.*]] ], [ 0, [[FOR_BODY_PREHEADER]] ]
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; CHECK-NEXT: [[IDXPROM:%.*]] = trunc i128 [[I_010]] to i64
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; CHECK-NEXT: [[ARRAYIDX:%.*]] = getelementptr inbounds i64, i64* [[A:%.*]], i64 [[IDXPROM]]
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; CHECK-NEXT: [[TMP0:%.*]] = load i64, i64* [[ARRAYIDX]]
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; CHECK-NEXT: [[ARRAYIDX2:%.*]] = getelementptr inbounds i64, i64* [[B:%.*]], i64 [[IDXPROM]]
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; CHECK-NEXT: [[TMP1:%.*]] = load i64, i64* [[ARRAYIDX2]]
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; CHECK-NEXT: [[CMP3:%.*]] = icmp eq i64 [[TMP0]], [[TMP1]]
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; CHECK-NEXT: [[INC]] = add nuw nsw i128 [[I_010]], 1
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; CHECK-NEXT: br i1 [[CMP3]], label [[FOR_COND]], label [[CLEANUP_LOOPEXIT]]
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; CHECK: cleanup.loopexit:
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; CHECK-NEXT: [[DOTPH:%.*]] = phi i64 [ 1, [[FOR_BODY]] ], [ 0, [[FOR_COND]] ]
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; CHECK-NEXT: br label [[CLEANUP]]
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; CHECK: cleanup:
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; CHECK-NEXT: [[TMP2:%.*]] = phi i64 [ 0, [[ENTRY:%.*]] ], [ [[DOTPH]], [[CLEANUP_LOOPEXIT]] ]
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; CHECK-NEXT: ret i64 [[TMP2]]
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;
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entry:
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%cmp9 = icmp sgt i128 %num, 0
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br i1 %cmp9, label %for.body, label %cleanup
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for.cond: ; preds = %for.body
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%cmp = icmp slt i128 %inc, %num
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br i1 %cmp, label %for.body, label %cleanup
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for.body: ; preds = %entry, %for.cond
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%i.010 = phi i128 [ %inc, %for.cond ], [ 0, %entry ]
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%idxprom = trunc i128 %i.010 to i64
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%arrayidx = getelementptr inbounds i64, i64* %a, i64 %idxprom
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%0 = load i64, i64* %arrayidx
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%arrayidx2 = getelementptr inbounds i64, i64* %b, i64 %idxprom
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%1 = load i64, i64* %arrayidx2
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%cmp3 = icmp eq i64 %0, %1
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%inc = add nuw nsw i128 %i.010, 1
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br i1 %cmp3, label %for.cond, label %cleanup
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cleanup: ; preds = %for.body, %for.cond, %entry
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%2 = phi i64 [ 0, %entry ], [ 0, %for.cond ], [ 1, %for.body ]
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ret i64 %2
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}
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