90ba33099c
This patch canonicalizes getelementptr instructions with constant indices to use the `i8` source element type. This makes it easier for optimizations to recognize that two GEPs are identical, because they don't need to see past many different ways to express the same offset. This is a first step towards https://discourse.llvm.org/t/rfc-replacing-getelementptr-with-ptradd/68699. This is limited to constant GEPs only for now, as they have a clear canonical form, while we're not yet sure how exactly to deal with variable indices. The test llvm/test/Transforms/PhaseOrdering/switch_with_geps.ll gives two representative examples of the kind of optimization improvement we expect from this change. In the first test SimplifyCFG can now realize that all switch branches are actually the same. In the second test it can convert it into simple arithmetic. These are representative of common optimization failures we see in Rust. Fixes https://github.com/llvm/llvm-project/issues/69841.
89 lines
3.6 KiB
LLVM
89 lines
3.6 KiB
LLVM
; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
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;
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; Verify that strlen calls with unterminated constant arrays or with
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; just past-the-end pointers to strings are not folded.
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;
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; RUN: opt < %s -passes=instcombine -S | FileCheck %s
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declare i64 @strlen(ptr)
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@a5 = constant [5 x i8] c"12345"
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@s5 = constant [6 x i8] c"12345\00"
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@z0 = constant [0 x i8] zeroinitializer
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@z5 = constant [5 x i8] zeroinitializer
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; Verify that all the invalid calls below are folded. This is safer than
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; making the library calls even though it prevents sanitizers from reporting
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; the bugs.
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define void @fold_strlen_no_nul(ptr %plen, i32 %i) {
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; CHECK-LABEL: @fold_strlen_no_nul(
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; CHECK-NEXT: store i64 5, ptr [[PLEN:%.*]], align 4
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; CHECK-NEXT: [[PNA5_P5:%.*]] = getelementptr i8, ptr [[PLEN]], i64 8
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; CHECK-NEXT: store i64 0, ptr [[PNA5_P5]], align 4
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; CHECK-NEXT: [[PNS5_P6:%.*]] = getelementptr i8, ptr [[PLEN]], i64 16
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; CHECK-NEXT: store i64 0, ptr [[PNS5_P6]], align 4
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; CHECK-NEXT: [[TMP1:%.*]] = sext i32 [[I:%.*]] to i64
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; CHECK-NEXT: [[PA5_PI:%.*]] = getelementptr [5 x i8], ptr @a5, i64 0, i64 [[TMP1]]
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; CHECK-NEXT: [[NA5_PI:%.*]] = call i64 @strlen(ptr noundef nonnull dereferenceable(1) [[PA5_PI]])
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; CHECK-NEXT: [[PNA5_PI:%.*]] = getelementptr i8, ptr [[PLEN]], i64 24
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; CHECK-NEXT: store i64 [[NA5_PI]], ptr [[PNA5_PI]], align 4
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; CHECK-NEXT: [[PNZ0_P0:%.*]] = getelementptr i8, ptr [[PLEN]], i64 32
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; CHECK-NEXT: store i64 0, ptr [[PNZ0_P0]], align 4
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; CHECK-NEXT: [[TMP2:%.*]] = sext i32 [[I]] to i64
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; CHECK-NEXT: [[PZ0_PI:%.*]] = getelementptr [0 x i8], ptr @z0, i64 0, i64 [[TMP2]]
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; CHECK-NEXT: [[NZ0_PI:%.*]] = call i64 @strlen(ptr noundef nonnull dereferenceable(1) [[PZ0_PI]])
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; CHECK-NEXT: [[PNZ0_PI:%.*]] = getelementptr i8, ptr [[PLEN]], i64 40
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; CHECK-NEXT: store i64 [[NZ0_PI]], ptr [[PNZ0_PI]], align 4
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; CHECK-NEXT: [[PNZ5_P5:%.*]] = getelementptr i8, ptr [[PLEN]], i64 48
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; CHECK-NEXT: store i64 0, ptr [[PNZ5_P5]], align 4
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; CHECK-NEXT: ret void
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;
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; Verify that strlen(a5) is folded to 5.
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%na5_p0 = call i64 @strlen(ptr @a5)
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store i64 %na5_p0, ptr %plen
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; Verify that strlen(a5 + 5) is folded to 0.
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%pa5_p5 = getelementptr [5 x i8], ptr @a5, i32 0, i32 5
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%na5_p5 = call i64 @strlen(ptr %pa5_p5)
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%pna5_p5 = getelementptr i64, ptr %plen, i64 1
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store i64 %na5_p5, ptr %pna5_p5
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; Verify that strlen(s5 + 6) is folded to 0.
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%ps5_p6 = getelementptr [6 x i8], ptr @s5, i32 0, i32 6
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%ns5_p6 = call i64 @strlen(ptr %ps5_p6)
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%pns5_p6 = getelementptr i64, ptr %plen, i64 2
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store i64 %ns5_p6, ptr %pns5_p6
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; TODO: Verify that strlen(a5 + i) is folded to 5 - i? It's currently
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; not folded because the variable offset makes getConstantDataArrayInfo
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; fail.
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%pa5_pi = getelementptr [5 x i8], ptr @a5, i32 0, i32 %i
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%na5_pi = call i64 @strlen(ptr %pa5_pi)
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%pna5_pi = getelementptr i64, ptr %plen, i64 3
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store i64 %na5_pi, ptr %pna5_pi
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; Verify that strlen(z0) is folded to 0.
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%nz0_p0 = call i64 @strlen(ptr @z0)
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%pnz0_p0 = getelementptr i64, ptr %plen, i64 4
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store i64 %nz0_p0, ptr %pnz0_p0
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; TODO: Verify that strlen(z0 + i) is folded to 0. As the case above,
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; this one is not folded either because the variable offset makes
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; getConstantDataArrayInfo fail.
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%pz0_pi = getelementptr [0 x i8], ptr @z0, i32 0, i32 %i
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%nz0_pi = call i64 @strlen(ptr %pz0_pi)
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%pnz0_pi = getelementptr i64, ptr %plen, i64 5
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store i64 %nz0_pi, ptr %pnz0_pi
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; Verify that strlen(z5 + 5) is folded to 0.
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%pz5_p5 = getelementptr [5 x i8], ptr @z5, i32 0, i32 5
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%nz5_p5 = call i64 @strlen(ptr %pz5_p5)
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%pnz5_p5 = getelementptr i64, ptr %plen, i64 6
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store i64 %nz5_p5, ptr %pnz5_p5
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ret void
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}
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