[PATCH] D67986: [InstCombine] snprintf (d, size, "%s", s) -> memccpy (d, s, '\0', size).
Dávid Bolvanský via Phabricator via llvm-commits
llvm-commits at lists.llvm.org
Tue Sep 24 14:26:48 PDT 2019
xbolva00 created this revision.
xbolva00 added reviewers: efriedma, jdoerfert.
Herald added a project: LLVM.
Herald added a subscriber: llvm-commits.
"By relying on memccpy optimizing compilers will be able to transform simple snprintf (d, dsize, "%s", s) calls into the optimally efficient calls to memccpy (d, s, '\0', dsize). "
Idea was presented in "Toward more efficient string copying and concatenation": http://www.open-std.org/jtc1/sc22/wg14/www/docs/n2349.htm
memccpy is part of C 20, so in the future it will be more useful than now. (only posix has memccpy now)
Repository:
rL LLVM
https://reviews.llvm.org/D67986
Files:
lib/Transforms/Utils/SimplifyLibCalls.cpp
test/Transforms/InstCombine/snprintf-memccpy.ll
Index: test/Transforms/InstCombine/snprintf-memccpy.ll
===================================================================
--- test/Transforms/InstCombine/snprintf-memccpy.ll
+++ test/Transforms/InstCombine/snprintf-memccpy.ll
@@ -0,0 +1,23 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt < %s -instcombine -S | FileCheck %s
+
+ at .str = private constant [3 x i8] c"%s\00", align 1
+declare i32 @snprintf(i8*, i64, i8*, ...)
+
+define i32 @test_string_to_buf_retval_used(i8* %buf, i64 %n, i8* %str) {
+; CHECK-LABEL: @test_string_to_buf_retval_used(
+; CHECK-NEXT: [[CALL:%.*]] = call i32 (i8*, i64, i8*, ...) @snprintf(i8* [[BUF:%.*]], i64 [[N:%.*]], i8* getelementptr inbounds ([3 x i8], [3 x i8]* @.str, i64 0, i64 0), i8* [[STR:%.*]])
+; CHECK-NEXT: ret i32 [[CALL]]
+;
+ %call = call i32 (i8*, i64, i8*, ...) @snprintf(i8* %buf, i64 %n, i8* getelementptr inbounds ([3 x i8], [3 x i8]* @.str, i64 0, i64 0), i8* %str)
+ ret i32 %call
+}
+
+define void @test_string_to_buf_retval_unused(i8* %buf, i64 %n, i8* %str) {
+; CHECK-LABEL: @test_string_to_buf_retval_unused(
+; CHECK-NEXT: [[MEMCCPY:%.*]] = call i8* @memccpy(i8* [[BUF:%.*]], i8* [[STR:%.*]], i32 0, i64 [[N:%.*]])
+; CHECK-NEXT: ret void
+;
+ %call = call i32 (i8*, i64, i8*, ...) @snprintf(i8* %buf, i64 %n, i8* getelementptr inbounds ([3 x i8], [3 x i8]* @.str, i64 0, i64 0), i8* %str)
+ ret void
+}
Index: lib/Transforms/Utils/SimplifyLibCalls.cpp
===================================================================
--- lib/Transforms/Utils/SimplifyLibCalls.cpp
+++ lib/Transforms/Utils/SimplifyLibCalls.cpp
@@ -2402,12 +2402,7 @@
}
Value *LibCallSimplifier::optimizeSnPrintFString(CallInst *CI, IRBuilder<> &B) {
- // Check for size
ConstantInt *Size = dyn_cast<ConstantInt>(CI->getArgOperand(1));
- if (!Size)
- return nullptr;
-
- uint64_t N = Size->getZExtValue();
// Check for a fixed format string.
StringRef FormatStr;
if (!getConstantStringInfo(CI->getArgOperand(2), FormatStr))
@@ -2420,6 +2415,9 @@
if (FormatStr.find('%') != StringRef::npos)
return nullptr; // we found a format specifier, bail out.
+ if (!Size)
+ return nullptr;
+ uint64_t N = Size->getZExtValue();
if (N == 0)
return ConstantInt::get(CI->getType(), FormatStr.size());
else if (N < FormatStr.size() + 1)
@@ -2441,6 +2439,9 @@
// Decode the second character of the format string.
if (FormatStr[1] == 'c') {
+ if (!Size)
+ return nullptr;
+ uint64_t N = Size->getZExtValue();
if (N == 0)
return ConstantInt::get(CI->getType(), 1);
else if (N == 1)
@@ -2461,9 +2462,17 @@
if (FormatStr[1] == 's') {
// snprintf(dest, size, "%s", str) to llvm.memcpy(dest, str, len+1, 1)
StringRef Str;
- if (!getConstantStringInfo(CI->getArgOperand(3), Str))
+ if (!getConstantStringInfo(CI->getArgOperand(3), Str)) {
+ if (CI->use_empty())
+ // snprintf (d, size, "%s", s) -> memccpy (d, s, '\0', size).
+ return emitMemCCpy(CI->getOperand(0), CI->getArgOperand(3),
+ B.getInt32('\0'), CI->getArgOperand(1), B, TLI);
return nullptr;
+ }
+ if (!Size)
+ return nullptr;
+ uint64_t N = Size->getZExtValue();
if (N == 0)
return ConstantInt::get(CI->getType(), Str.size());
else if (N < Str.size() + 1)
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