maxjhandsome
/
llvm-project
forked from OSchip/llvm-project
1
0
Fork 0
Code Issues Pull Requests Packages Releases Wiki Activity
llvm-project/llvm/test/Transforms/InstCombine/compare-alloca.ll

98 lines
2.8 KiB
LLVM
Raw Normal View History

InstCombine: Fold comparisons between unguessable allocas and other pointers This will allow us to optimize code such as: int f(int *p) { int x; return p == &x; } as well as: int *allocate(void); int f() { int x; int *p = allocate(); return p == &x; } The folding can only be done under certain circumstances. Even though p and &x cannot alias, the comparison must still return true if the pointer representations are equal. If a user successfully generates a p that's a correct guess for &x, comparison should return true even though p is an invalid pointer. This patch argues that if the address of the alloca isn't observable outside the function, the function can act as-if the address is impossible to guess from the outside. The tricky part is keeping the act consistent: if we fold p == &x to false in one place, we must make sure to fold any other comparisons based on those pointers similarly. To ensure that, we only fold when &x is involved exactly once in comparison instructions. Differential Revision: http://reviews.llvm.org/D13358 llvm-svn: 249490
2015-10-07 08:20:07 +08:00
; RUN: opt -instcombine -S %s | FileCheck %s
target datalayout = "p:32:32"
define i1 @alloca_argument_compare(i64* %arg) {
%alloc = alloca i64
%cmp = icmp eq i64* %arg, %alloc
ret i1 %cmp
; CHECK-LABEL: alloca_argument_compare
; CHECK: ret i1 false
}
define i1 @alloca_argument_compare_swapped(i64* %arg) {
%alloc = alloca i64
%cmp = icmp eq i64* %alloc, %arg
ret i1 %cmp
; CHECK-LABEL: alloca_argument_compare_swapped
; CHECK: ret i1 false
}
define i1 @alloca_argument_compare_ne(i64* %arg) {
%alloc = alloca i64
%cmp = icmp ne i64* %arg, %alloc
ret i1 %cmp
; CHECK-LABEL: alloca_argument_compare_ne
; CHECK: ret i1 true
}
define i1 @alloca_argument_compare_derived_ptrs(i64* %arg, i64 %x) {
%alloc = alloca i64, i64 8
%p = getelementptr i64, i64* %arg, i64 %x
%q = getelementptr i64, i64* %alloc, i64 3
%cmp = icmp eq i64* %p, %q
ret i1 %cmp
; CHECK-LABEL: alloca_argument_compare_derived_ptrs
; CHECK: ret i1 false
}
declare void @escape(i64*)
define i1 @alloca_argument_compare_escaped_alloca(i64* %arg) {
%alloc = alloca i64
call void @escape(i64* %alloc)
%cmp = icmp eq i64* %alloc, %arg
ret i1 %cmp
; CHECK-LABEL: alloca_argument_compare_escaped_alloca
; CHECK: %cmp = icmp eq i64* %alloc, %arg
; CHECK: ret i1 %cmp
}
declare void @check_compares(i1, i1)
define void @alloca_argument_compare_two_compares(i64* %p) {
%q = alloca i64, i64 8
%r = getelementptr i64, i64* %p, i64 1
%s = getelementptr i64, i64* %q, i64 2
%cmp1 = icmp eq i64* %p, %q
%cmp2 = icmp eq i64* %r, %s
call void @check_compares(i1 %cmp1, i1 %cmp2)
ret void
; We will only fold if there is a single cmp.
; CHECK-LABEL: alloca_argument_compare_two_compares
; CHECK: call void @check_compares(i1 %cmp1, i1 %cmp2)
}
define i1 @alloca_argument_compare_escaped_through_store(i64* %arg, i64** %ptr) {
%alloc = alloca i64
%cmp = icmp eq i64* %alloc, %arg
%p = getelementptr i64, i64* %alloc, i64 1
store i64* %p, i64** %ptr
ret i1 %cmp
; CHECK-LABEL: alloca_argument_compare_escaped_through_store
; CHECK: %cmp = icmp eq i64* %alloc, %arg
; CHECK: ret i1 %cmp
}
declare void @llvm.lifetime.start(i64, i8* nocapture)
declare void @llvm.lifetime.end(i64, i8* nocapture)
define i1 @alloca_argument_compare_benign_instrs(i8* %arg) {
%alloc = alloca i8
call void @llvm.lifetime.start(i64 1, i8* %alloc)
%cmp = icmp eq i8* %arg, %alloc
%x = load i8, i8* %arg
store i8 %x, i8* %alloc
call void @llvm.lifetime.end(i64 1, i8* %alloc)
ret i1 %cmp
; CHECK-LABEL: alloca_argument_compare_benign_instrs
; CHECK: ret i1 false
}
declare i64* @allocator()
define i1 @alloca_call_compare() {
%p = alloca i64
%q = call i64* @allocator()
%cmp = icmp eq i64* %p, %q
ret i1 %cmp
; CHECK-LABEL: alloca_call_compare
; CHECK: ret i1 false
}