[InstCombine] snprintf optimizations
Reviewers: spatel, efriedma, majnemer, rja, bkramer
Reviewed By: rja, bkramer
Subscribers: mstorsjo, rja, llvm-commits
Differential Revision: https://reviews.llvm.org/D46285
llvm-svn: 332110
diff --git a/llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp b/llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
index ce804ae..6e351d4 100644
--- a/llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
@@ -1912,6 +1912,94 @@
return nullptr;
}
+Value *LibCallSimplifier::optimizeSnPrintFString(CallInst *CI, IRBuilder<> &B) {
+ // Check for a fixed format string.
+ StringRef FormatStr;
+ if (!getConstantStringInfo(CI->getArgOperand(2), FormatStr))
+ return nullptr;
+
+ // Check for size
+ ConstantInt *Size = dyn_cast<ConstantInt>(CI->getArgOperand(1));
+ if (!Size)
+ return nullptr;
+
+ uint64_t N = Size->getZExtValue();
+
+ // If we just have a format string (nothing else crazy) transform it.
+ if (CI->getNumArgOperands() == 3) {
+ // Make sure there's no % in the constant array. We could try to handle
+ // %% -> % in the future if we cared.
+ for (unsigned i = 0, e = FormatStr.size(); i != e; ++i)
+ if (FormatStr[i] == '%')
+ return nullptr; // we found a format specifier, bail out.
+
+ if (N == 0)
+ return ConstantInt::get(CI->getType(), FormatStr.size());
+ else if (N < FormatStr.size() + 1)
+ return nullptr;
+
+ // sprintf(str, size, fmt) -> llvm.memcpy(align 1 str, align 1 fmt,
+ // strlen(fmt)+1)
+ B.CreateMemCpy(
+ CI->getArgOperand(0), 1, CI->getArgOperand(2), 1,
+ ConstantInt::get(DL.getIntPtrType(CI->getContext()),
+ FormatStr.size() + 1)); // Copy the null byte.
+ return ConstantInt::get(CI->getType(), FormatStr.size());
+ }
+
+ // The remaining optimizations require the format string to be "%s" or "%c"
+ // and have an extra operand.
+ if (FormatStr.size() == 2 && FormatStr[0] == '%' &&
+ CI->getNumArgOperands() == 4) {
+
+ // Decode the second character of the format string.
+ if (FormatStr[1] == 'c') {
+ if (N == 0)
+ return ConstantInt::get(CI->getType(), 1);
+ else if (N == 1)
+ return nullptr;
+
+ // snprintf(dst, size, "%c", chr) --> *(i8*)dst = chr; *((i8*)dst+1) = 0
+ if (!CI->getArgOperand(3)->getType()->isIntegerTy())
+ return nullptr;
+ Value *V = B.CreateTrunc(CI->getArgOperand(3), B.getInt8Ty(), "char");
+ Value *Ptr = castToCStr(CI->getArgOperand(0), B);
+ B.CreateStore(V, Ptr);
+ Ptr = B.CreateGEP(B.getInt8Ty(), Ptr, B.getInt32(1), "nul");
+ B.CreateStore(B.getInt8(0), Ptr);
+
+ return ConstantInt::get(CI->getType(), 1);
+ }
+
+ 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))
+ return nullptr;
+
+ if (N == 0)
+ return ConstantInt::get(CI->getType(), Str.size());
+ else if (N < Str.size() + 1)
+ return nullptr;
+
+ B.CreateMemCpy(CI->getArgOperand(0), 1, CI->getArgOperand(3), 1,
+ ConstantInt::get(CI->getType(), Str.size() + 1));
+
+ // The snprintf result is the unincremented number of bytes in the string.
+ return ConstantInt::get(CI->getType(), Str.size());
+ }
+ }
+ return nullptr;
+}
+
+Value *LibCallSimplifier::optimizeSnPrintF(CallInst *CI, IRBuilder<> &B) {
+ if (Value *V = optimizeSnPrintFString(CI, B)) {
+ return V;
+ }
+
+ return nullptr;
+}
+
Value *LibCallSimplifier::optimizeFPrintFString(CallInst *CI, IRBuilder<> &B) {
optimizeErrorReporting(CI, B, 0);
@@ -2318,6 +2406,8 @@
return optimizePrintF(CI, Builder);
case LibFunc_sprintf:
return optimizeSPrintF(CI, Builder);
+ case LibFunc_snprintf:
+ return optimizeSnPrintF(CI, Builder);
case LibFunc_fprintf:
return optimizeFPrintF(CI, Builder);
case LibFunc_fwrite: