Author: Fangrui Song Date: 2020-10-15T15:14:38-07:00 New Revision: 5a338599fbaa805587227779bde0a9986cb4646d
URL: https://github.com/llvm/llvm-project/commit/5a338599fbaa805587227779bde0a9986cb4646d DIFF: https://github.com/llvm/llvm-project/commit/5a338599fbaa805587227779bde0a9986cb4646d.diff LOG: [CGBuiltin] Respect asm labels and redefine_extname for builtins with specialized emitting rL131311 added `asm()` support for builtin functions, but `asm()` for builtins with specialized emitting (e.g. memcpy, various math functions) still do not work. This patch makes these functions work for `asm()` and `#pragma redefine_extname`. glibc uses `asm()` to redirect internal libc function calls to hidden aliases. Limitation: such a function is a builtin in clang, but will not be recognized as a libcall in optimization passes because Clang does not annotate the renamed function as a libcall. In GCC -O1 or above, `abs` can be optimized out but we can't. Additionally, we cannot redirect `__builtin_sin` to `real_sin` in the following example: double sin(double x) asm("real_sin"); double f(double d) { return __builtin_sin(d); } --- According to @rsmith, the following three statements cannot be simultaneously true: (1) The frontend function foo has known, builtin semantics X. (2) The symbol foo has known, builtin semantics X. (3) It's not correct to lower a call to the frontend function foo to the symbol foo. People do want (1) (if it is profitable to expand a memcpy, do it). This also means that people do not want to add -fno-builtin-memcpy. People do want (3): that is why they use asm("__GI_memcpy") in the first place. So unfortunately we make a compromise by not refuting (2) (see the limitation above). For most libcalls, there is a small loss because compilers don't synthesize them. For the few glibc cares about, it uses `asm("memcpy = __GI_memcpy");` to make the assembly level redirection. (Changing function names (e.g. `__memcpy`) is a hit to ergonomics which is not acceptable). Reviewed By: rsmith Differential Revision: https://reviews.llvm.org/D88712 Added: Modified: clang/lib/CodeGen/CGBuiltin.cpp clang/test/CodeGen/asm-label.c clang/test/CodeGen/redefine_extname.c Removed: ################################################################################ diff --git a/clang/lib/CodeGen/CGBuiltin.cpp b/clang/lib/CodeGen/CGBuiltin.cpp index 884fa1103163..90bfeefc9970 100644 --- a/clang/lib/CodeGen/CGBuiltin.cpp +++ b/clang/lib/CodeGen/CGBuiltin.cpp @@ -1663,13 +1663,20 @@ RValue CodeGenFunction::EmitBuiltinExpr(const GlobalDecl GD, unsigned BuiltinID, Result.Val.getFloat())); } + // If the builtin has been declared explicitly with an assembler label, + // disable the specialized emitting below. Ideally we should communicate the + // rename in IR, or at least avoid generating the intrinsic calls that are + // likely to get lowered to the renamed library functions. + const unsigned BuiltinIDIfNoAsmLabel = + FD->hasAttr<AsmLabelAttr>() ? 0 : BuiltinID; + // There are LLVM math intrinsics/instructions corresponding to math library // functions except the LLVM op will never set errno while the math library // might. Also, math builtins have the same semantics as their math library // twins. Thus, we can transform math library and builtin calls to their // LLVM counterparts if the call is marked 'const' (known to never set errno). if (FD->hasAttr<ConstAttr>()) { - switch (BuiltinID) { + switch (BuiltinIDIfNoAsmLabel) { case Builtin::BIceil: case Builtin::BIceilf: case Builtin::BIceill: @@ -1946,7 +1953,7 @@ RValue CodeGenFunction::EmitBuiltinExpr(const GlobalDecl GD, unsigned BuiltinID, } } - switch (BuiltinID) { + switch (BuiltinIDIfNoAsmLabel) { default: break; case Builtin::BI__builtin___CFStringMakeConstantString: case Builtin::BI__builtin___NSStringMakeConstantString: diff --git a/clang/test/CodeGen/asm-label.c b/clang/test/CodeGen/asm-label.c index 7c7383fa41fc..093f31fc59c4 100644 --- a/clang/test/CodeGen/asm-label.c +++ b/clang/test/CodeGen/asm-label.c @@ -1,5 +1,5 @@ -// RUN: %clang_cc1 -triple=i686-pc-linux-gnu -emit-llvm %s -o - | FileCheck %s --check-prefix=LINUX -// RUN: %clang_cc1 -triple=i686-apple-darwin9 -emit-llvm %s -o - | FileCheck %s --check-prefix=DARWIN +// RUN: %clang_cc1 -triple=i686-pc-linux-gnu -emit-llvm %s -o - | FileCheck %s --check-prefixes=CHECK,LINUX +// RUN: %clang_cc1 -triple=i686-apple-darwin9 -emit-llvm %s -o - | FileCheck %s --check-prefixes=CHECK,DARWIN char *strerror(int) asm("alias"); int x __asm("foo"); @@ -17,3 +17,39 @@ int *test(void) { // DARWIN: @"\01bar" = internal global i32 0 // DARWIN: @"\01foo" = global i32 0 // DARWIN: declare i8* @"\01alias"(i32) + +extern void *memcpy(void *__restrict, const void *__restrict, unsigned long); +extern __typeof(memcpy) memcpy asm("__GI_memcpy"); +void test_memcpy(void *dst, void *src, unsigned long n) { + memcpy(dst, src, n); +} +// CHECK-LABEL: @test_memcpy( +// LINUX: call i8* @__GI_memcpy( +// LINUX: declare i8* @__GI_memcpy(i8*, i8*, i32) +// DARWIN: call i8* @"\01__GI_memcpy"( +// DARWIN: declare i8* @"\01__GI_memcpy"(i8*, i8*, i32) + +long lrint(double x) asm("__GI_lrint"); +long test_lrint(double x) { + return lrint(x); +} +// CHECK-LABEL: @test_lrint( +// LINUX: call i32 @__GI_lrint( +// LINUX: declare i32 @__GI_lrint(double) +// DARWIN: call i32 @"\01__GI_lrint"( +// DARWIN: declare i32 @"\01__GI_lrint"(double) + +/// NOTE: GCC can optimize out abs in -O1 or above. Clang does not +/// communicate the mapping to the backend so the libcall cannot be eliminated. +int abs(int x) asm("__GI_abs"); +long test_abs(int x) { + return abs(x); +} +// CHECK-LABEL: @test_abs( +// LINUX: call i32 @__GI_abs( + +/// FIXME: test_sin should call real_sin instead. +double sin(double x) asm("real_sin"); +double test_sin(double d) { return __builtin_sin(d); } +// CHECK-LABEL: @test_sin( +// LINUX: call double @llvm.sin.f64( diff --git a/clang/test/CodeGen/redefine_extname.c b/clang/test/CodeGen/redefine_extname.c index d56527a88953..5661df546991 100644 --- a/clang/test/CodeGen/redefine_extname.c +++ b/clang/test/CodeGen/redefine_extname.c @@ -30,3 +30,9 @@ static int foo_static() { return 1; } int baz() { return foo_static(); } // CHECK-NOT: call i32 @bar_static() +// Check that pragma redefine_extname applies to builtin functions. +typedef unsigned long size_t; +extern void *memcpy(void *, const void *, size_t); +#pragma redefine_extname memcpy __GI_memcpy +void *test_memcpy(void *dst, const void *src, size_t n) { return memcpy(dst, src, n); } +// CHECK: call i8* @__GI_memcpy( _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
