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llvm-project/llvm/test/Transforms/InstCombine/strlen-7.ll
Nikita Popov 90ba33099c
[InstCombine] Canonicalize constant GEPs to i8 source element type (#68882) 
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.
2024-01-24 15:25:29 +01:00

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; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
; Verify that strlen calls with members of constant structs are folded.
;
; RUN: opt < %s -passes=instcombine -S | FileCheck %s
declare i64 @strlen(ptr)
%struct.A = type { [4 x i8], [5 x i8] }
@a = constant [2 x %struct.A] [%struct.A { [4 x i8] c"1\00\00\00", [5 x i8] c"12\00\00\00" }, %struct.A { [4 x i8] c"123\00", [5 x i8] c"1234\00" }], align 16
; Fold strlen(a[I].a + J) and strlen(a[I].b + J) with constant I and J
; to constants.
define void @fold_strlen_A(ptr %plen) {
; CHECK-LABEL: @fold_strlen_A(
; CHECK-NEXT: store i64 1, ptr [[PLEN:%.*]], align 4
; CHECK-NEXT: [[PLEN1:%.*]] = getelementptr i8, ptr [[PLEN]], i64 8
; CHECK-NEXT: store i64 0, ptr [[PLEN1]], align 4
; CHECK-NEXT: [[PLEN2:%.*]] = getelementptr i8, ptr [[PLEN]], i64 16
; CHECK-NEXT: store i64 0, ptr [[PLEN2]], align 4
; CHECK-NEXT: [[PLEN3:%.*]] = getelementptr i8, ptr [[PLEN]], i64 24
; CHECK-NEXT: store i64 0, ptr [[PLEN3]], align 4
; CHECK-NEXT: [[PLEN4:%.*]] = getelementptr i8, ptr [[PLEN]], i64 32
; CHECK-NEXT: store i64 2, ptr [[PLEN4]], align 4
; CHECK-NEXT: [[PLEN5:%.*]] = getelementptr i8, ptr [[PLEN]], i64 40
; CHECK-NEXT: store i64 1, ptr [[PLEN5]], align 4
; CHECK-NEXT: [[PLEN6:%.*]] = getelementptr i8, ptr [[PLEN]], i64 48
; CHECK-NEXT: store i64 0, ptr [[PLEN6]], align 4
; CHECK-NEXT: [[PLEN7:%.*]] = getelementptr i8, ptr [[PLEN]], i64 56
; CHECK-NEXT: store i64 0, ptr [[PLEN7]], align 4
; CHECK-NEXT: [[PLEN8:%.*]] = getelementptr i8, ptr [[PLEN]], i64 64
; CHECK-NEXT: store i64 0, ptr [[PLEN8]], align 4
; CHECK-NEXT: [[PLEN9:%.*]] = getelementptr i8, ptr [[PLEN]], i64 72
; CHECK-NEXT: store i64 3, ptr [[PLEN9]], align 4
; CHECK-NEXT: [[PLEN10:%.*]] = getelementptr i8, ptr [[PLEN]], i64 80
; CHECK-NEXT: store i64 2, ptr [[PLEN10]], align 4
; CHECK-NEXT: [[PLEN11:%.*]] = getelementptr i8, ptr [[PLEN]], i64 88
; CHECK-NEXT: store i64 1, ptr [[PLEN11]], align 4
; CHECK-NEXT: [[PLEN12:%.*]] = getelementptr i8, ptr [[PLEN]], i64 96
; CHECK-NEXT: store i64 0, ptr [[PLEN12]], align 4
; CHECK-NEXT: [[PLEN14:%.*]] = getelementptr i8, ptr [[PLEN]], i64 112
; CHECK-NEXT: store i64 4, ptr [[PLEN14]], align 4
; CHECK-NEXT: [[PLEN15:%.*]] = getelementptr i8, ptr [[PLEN]], i64 120
; CHECK-NEXT: store i64 3, ptr [[PLEN15]], align 4
; CHECK-NEXT: [[PLEN16:%.*]] = getelementptr i8, ptr [[PLEN]], i64 128
; CHECK-NEXT: store i64 2, ptr [[PLEN16]], align 4
; CHECK-NEXT: [[PLEN17:%.*]] = getelementptr i8, ptr [[PLEN]], i64 136
; CHECK-NEXT: store i64 1, ptr [[PLEN17]], align 4
; CHECK-NEXT: [[PLEN18:%.*]] = getelementptr i8, ptr [[PLEN]], i64 144
; CHECK-NEXT: store i64 0, ptr [[PLEN18]], align 4
; CHECK-NEXT: ret void
;
; Fold strlen(a[0].a) to 1.
%lena0a = call i64 @strlen(ptr @a)
store i64 %lena0a, ptr %plen
; Fold strlen(a[0].a + 1) to 0.
%pa0ap1 = getelementptr [2 x %struct.A], ptr @a, i64 0, i64 0, i32 0, i64 1
%lena0ap1 = call i64 @strlen(ptr %pa0ap1)
%plen1 = getelementptr i64, ptr %plen, i32 1
store i64 %lena0ap1, ptr %plen1
; Fold strlen(a[0].a + 2) to 0.
%pa0ap2 = getelementptr [2 x %struct.A], ptr @a, i64 0, i64 0, i32 0, i64 2
%lena0ap2 = call i64 @strlen(ptr %pa0ap2)
%plen2 = getelementptr i64, ptr %plen, i32 2
store i64 %lena0ap2, ptr %plen2
; Fold strlen(a[0].a + 3) to 0.
%pa0ap3 = getelementptr [2 x %struct.A], ptr @a, i64 0, i64 0, i32 0, i64 3
%lena0ap3 = call i64 @strlen(ptr %pa0ap3)
%plen3 = getelementptr i64, ptr %plen, i32 3
store i64 %lena0ap3, ptr %plen3
; Fold strlen(a[0].b) to 2.
%pa0b = getelementptr [2 x %struct.A], ptr @a, i64 0, i64 0, i32 1, i64 0
%lena0b = call i64 @strlen(ptr %pa0b)
%plen4 = getelementptr i64, ptr %plen, i32 4
store i64 %lena0b, ptr %plen4
; Fold strlen(a[0].b + 1) to 1.
%pa0bp1 = getelementptr [2 x %struct.A], ptr @a, i64 0, i64 0, i32 1, i64 1
%lena0bp1 = call i64 @strlen(ptr %pa0bp1)
%plen5 = getelementptr i64, ptr %plen, i32 5
store i64 %lena0bp1, ptr %plen5
; Fold strlen(a[0].b + 2) to 0.
%pa0bp2 = getelementptr [2 x %struct.A], ptr @a, i64 0, i64 0, i32 1, i64 2
%lena0bp2 = call i64 @strlen(ptr %pa0bp2)
%plen6 = getelementptr i64, ptr %plen, i32 6
store i64 %lena0bp2, ptr %plen6
; Fold strlen(a[0].b + 3) to 0.
%pa0bp3 = getelementptr [2 x %struct.A], ptr @a, i64 0, i64 0, i32 1, i64 3
%lena0bp3 = call i64 @strlen(ptr %pa0bp3)
%plen7 = getelementptr i64, ptr %plen, i32 7
store i64 %lena0bp3, ptr %plen7
; Fold strlen(a[0].b + 4) to 0.
%pa0bp4 = getelementptr [2 x %struct.A], ptr @a, i64 0, i64 0, i32 1, i64 4
%lena0bp4 = call i64 @strlen(ptr %pa0bp4)
%plen8 = getelementptr i64, ptr %plen, i32 8
store i64 %lena0bp4, ptr %plen8
; Fold strlen(a[1].a) to 3.
%pa1a = getelementptr [2 x %struct.A], ptr @a, i64 0, i64 1, i32 0, i64 0
%lena1a = call i64 @strlen(ptr %pa1a)
%plen9 = getelementptr i64, ptr %plen, i32 9
store i64 %lena1a, ptr %plen9
; Fold strlen(a[1].a + 1) to 2.
%pa1ap1 = getelementptr [2 x %struct.A], ptr @a, i64 0, i64 1, i32 0, i64 1
%lena1ap1 = call i64 @strlen(ptr %pa1ap1)
%plen10 = getelementptr i64, ptr %plen, i32 10
store i64 %lena1ap1, ptr %plen10
; Fold strlen(a[1].a + 2) to 1.
%pa1ap2 = getelementptr [2 x %struct.A], ptr @a, i64 0, i64 1, i32 0, i64 2
%lena1ap2 = call i64 @strlen(ptr %pa1ap2)
%plen11 = getelementptr i64, ptr %plen, i32 11
store i64 %lena1ap2, ptr %plen11
; Fold strlen(a[1].a + 3) to 0.
%pa1ap3 = getelementptr [2 x %struct.A], ptr @a, i64 0, i64 1, i32 0, i64 3
%lena1ap3 = call i64 @strlen(ptr %pa1ap3)
%plen12 = getelementptr i64, ptr %plen, i32 12
store i64 %lena1ap3, ptr %plen12
; Fold strlen(a[1].b) to 4.
%pa1b = getelementptr [2 x %struct.A], ptr @a, i64 0, i64 1, i32 1, i64 0
%lena1b = call i64 @strlen(ptr %pa1b)
%plen14 = getelementptr i64, ptr %plen, i32 14
store i64 %lena1b, ptr %plen14
; Fold strlen(a[1].b + 1) to 3.
%pa1bp1 = getelementptr [2 x %struct.A], ptr @a, i64 0, i64 1, i32 1, i64 1
%lena1bp1 = call i64 @strlen(ptr %pa1bp1)
%plen15 = getelementptr i64, ptr %plen, i32 15
store i64 %lena1bp1, ptr %plen15
; Fold strlen(a[1].b + 2) to 2.
%pa1bp2 = getelementptr [2 x %struct.A], ptr @a, i64 0, i64 1, i32 1, i64 2
%lena1bp2 = call i64 @strlen(ptr %pa1bp2)
%plen16 = getelementptr i64, ptr %plen, i32 16
store i64 %lena1bp2, ptr %plen16
; Fold strlen(a[1].b + 3) to 1.
%pa1bp3 = getelementptr [2 x %struct.A], ptr @a, i64 0, i64 1, i32 1, i64 3
%lena1bp3 = call i64 @strlen(ptr %pa1bp3)
%plen17 = getelementptr i64, ptr %plen, i32 17
store i64 %lena1bp3, ptr %plen17
; Fold strlen(a[1].b + 4) to 0.
%pa1bp4 = getelementptr [2 x %struct.A], ptr @a, i64 0, i64 1, i32 1, i64 4
%lena1bp4 = call i64 @strlen(ptr %pa1bp4)
%plen18 = getelementptr i64, ptr %plen, i32 18
store i64 %lena1bp4, ptr %plen18
ret void
}
; TODO: Fold strlen(a[I].a + X) and strlen(a[I].b + X) with constant I and
; variable X to (X - strlen(a[I].a)) and (X - strlen(a[I].b)) respectively.
define void @fold_strlen_A_pI(ptr %plen, i64 %I) {
; CHECK-LABEL: @fold_strlen_A_pI(
; CHECK-NEXT: [[PA0A:%.*]] = getelementptr [2 x %struct.A], ptr @a, i64 0, i64 0, i32 0, i64 [[I:%.*]]
; CHECK-NEXT: [[LENA0A:%.*]] = call i64 @strlen(ptr noundef nonnull dereferenceable(1) [[PA0A]])
; CHECK-NEXT: store i64 [[LENA0A]], ptr [[PLEN:%.*]], align 4
; CHECK-NEXT: [[PA0B:%.*]] = getelementptr [2 x %struct.A], ptr @a, i64 0, i64 0, i32 1, i64 [[I]]
; CHECK-NEXT: [[LENA0B:%.*]] = call i64 @strlen(ptr noundef nonnull dereferenceable(1) [[PA0B]])
; CHECK-NEXT: [[PLEN1:%.*]] = getelementptr i8, ptr [[PLEN]], i64 8
; CHECK-NEXT: store i64 [[LENA0B]], ptr [[PLEN1]], align 4
; CHECK-NEXT: [[PA1A:%.*]] = getelementptr [2 x %struct.A], ptr @a, i64 0, i64 1, i32 0, i64 [[I]]
; CHECK-NEXT: [[LENA1A:%.*]] = call i64 @strlen(ptr noundef nonnull dereferenceable(1) [[PA1A]])
; CHECK-NEXT: [[PLEN2:%.*]] = getelementptr i8, ptr [[PLEN]], i64 16
; CHECK-NEXT: store i64 [[LENA1A]], ptr [[PLEN2]], align 4
; CHECK-NEXT: [[PA1B:%.*]] = getelementptr [2 x %struct.A], ptr @a, i64 0, i64 1, i32 1, i64 [[I]]
; CHECK-NEXT: [[LENA1B:%.*]] = call i64 @strlen(ptr noundef nonnull dereferenceable(1) [[PA1B]])
; CHECK-NEXT: [[PLEN3:%.*]] = getelementptr i8, ptr [[PLEN]], i64 24
; CHECK-NEXT: store i64 [[LENA1B]], ptr [[PLEN3]], align 4
; CHECK-NEXT: ret void
;
%pa0a = getelementptr [2 x %struct.A], ptr @a, i64 0, i64 0, i32 0, i64 %I
%lena0a = call i64 @strlen(ptr %pa0a)
store i64 %lena0a, ptr %plen
%pa0b = getelementptr [2 x %struct.A], ptr @a, i64 0, i64 0, i32 1, i64 %I
%lena0b = call i64 @strlen(ptr %pa0b)
%plen1 = getelementptr i64, ptr %plen, i32 1
store i64 %lena0b, ptr %plen1
%pa1a = getelementptr [2 x %struct.A], ptr @a, i64 0, i64 1, i32 0, i64 %I
%lena1a = call i64 @strlen(ptr %pa1a)
%plen2 = getelementptr i64, ptr %plen, i32 2
store i64 %lena1a, ptr %plen2
%pa1b = getelementptr [2 x %struct.A], ptr @a, i64 0, i64 1, i32 1, i64 %I
%lena1b = call i64 @strlen(ptr %pa1b)
%plen3 = getelementptr i64, ptr %plen, i32 3
store i64 %lena1b, ptr %plen3
ret void
}
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