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llvm-project/clang/test/CodeGen/builtin-count-zeros.c

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Make clz/ctz builtins defined for zero on ARM targets. rdar://10732455 ARM supports clz and ctz directly and both operations have well-defined results for zero. There is no disadvantage in performance to using the defined-at-zero versions of llvm.ctlz/cttz intrinsics. We're running into ARM-specific code written with the assumption that __builtin_clz(0) == 32, even though that value is technically undefined. The code is failing now because of llvm optimizations that are taking advantage of the undef behavior (specifically svn r147255). There's nothing wrong with that optimization on x86 where any incorrect assumptions about __builtin_clz(0) will quickly be exposed. For ARM, though, optimizations based on that undef behavior are likely to cause subtle bugs. Other targets with defined-at-zero clz/ctz support may want to override the default behavior as well. llvm-svn: 149086
2012-01-27 06:14:27 +08:00
// RUN: %clang_cc1 -triple x86_64-unknown-unknown -emit-llvm %s -o - | FileCheck %s
// RUN: %clang_cc1 -triple arm-unknown-unknown -emit-llvm %s -o - | FileCheck %s --check-prefix=CHECK-ARM
Implementation of __builtin_ctlz. llvm-svn: 51595
2008-05-27 23:32:46 +08:00
int a(int a) {return __builtin_ctz(a) + __builtin_clz(a);}
Make clz/ctz builtins defined for zero on ARM targets. rdar://10732455 ARM supports clz and ctz directly and both operations have well-defined results for zero. There is no disadvantage in performance to using the defined-at-zero versions of llvm.ctlz/cttz intrinsics. We're running into ARM-specific code written with the assumption that __builtin_clz(0) == 32, even though that value is technically undefined. The code is failing now because of llvm optimizations that are taking advantage of the undef behavior (specifically svn r147255). There's nothing wrong with that optimization on x86 where any incorrect assumptions about __builtin_clz(0) will quickly be exposed. For ARM, though, optimizations based on that undef behavior are likely to cause subtle bugs. Other targets with defined-at-zero clz/ctz support may want to override the default behavior as well. llvm-svn: 149086
2012-01-27 06:14:27 +08:00
// CHECK: call i32 @llvm.cttz.i32({{.*}}, i1 true)
// CHECK: call i32 @llvm.ctlz.i32({{.*}}, i1 true)
// CHECK-ARM: call i32 @llvm.cttz.i32({{.*}}, i1 false)
// CHECK-ARM: call i32 @llvm.ctlz.i32({{.*}}, i1 false)