[PATCH] D100724: [SimplifyLibCalls] Transform printf("%s", str) to puts(str) or noop.

[Dawid Jurczak via Phabricator via llvm-commits]

yurai007 updated this revision to Diff 339585.
yurai007 retitled this revision from "[SimplifyLibCalls] Transform printf("%s", str"\n") --> puts(str)." to "[SimplifyLibCalls] Transform printf("%s", str) to puts(str) or noop.".
yurai007 edited the summary of this revision.

Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D100724/new/

https://reviews.llvm.org/D100724

Files:
  llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
  llvm/test/Transforms/InstCombine/printf-2.ll


Index: llvm/test/Transforms/InstCombine/printf-2.ll
===================================================================
--- llvm/test/Transforms/InstCombine/printf-2.ll
+++ llvm/test/Transforms/InstCombine/printf-2.ll
@@ -10,6 +10,7 @@
 @percent_s = constant [4 x i8] c"%s\0A\00"
 @format_str = constant [3 x i8] c"%s\00"
 @charstr = constant [2 x i8] c"a\00"
+ at empty = constant [1 x i8] c"\00"
 
 declare void @printf(i8*, ...)
 
@@ -56,3 +57,48 @@
   call void (i8*, ...) @printf(i8* %fmt, i8* %str)
   ret void
 }
+
+; printf("%s", "") --> noop
+
+define void @test_simplify8() {
+; CHECK-LABEL: @test_simplify8(
+; CHECK-NEXT:    ret void
+;
+  %fmt = getelementptr [3 x i8], [3 x i8]* @format_str, i32 0, i32 0
+  %str = getelementptr [1 x i8], [1 x i8]* @empty, i32 0, i32 0
+  call void (i8*, ...) @printf(i8* %fmt, i8* %str)
+  ret void
+}
+
+; printf("%s", str"\n") --> puts(str)
+
+define void @test_simplify9() {
+; CHECK-LABEL: @test_simplify9(
+; CHECK-NEXT:    [[PUTS:%.*]] = call i32 @puts(i8* nonnull dereferenceable(1) getelementptr inbounds ([12 x i8], [12 x i8]* @str.1, i32 0, i32 0))
+; CHECK-NEXT:    ret void
+;
+  %fmt = getelementptr [3 x i8], [3 x i8]* @format_str, i32 0, i32 0
+  %str = getelementptr [13 x i8], [13 x i8]* @hello_world, i32 0, i32 0
+  call void (i8*, ...) @printf(i8* %fmt, i8* %str)
+  ret void
+}
+
+; printf("%s", "", ...) --> noop
+; printf("%s", "a", ...) --> putchar('a')
+; printf("%s", str"\n", ...) --> puts(str)
+
+define void @test_simplify10() {
+; CHECK-LABEL: @test_simplify10(
+; CHECK-NEXT:    [[PUTCHAR:%.*]] = call i32 @putchar(i32 97)
+; CHECK-NEXT:    [[PUTS:%.*]] = call i32 @puts(i8* nonnull dereferenceable(1) getelementptr inbounds ([12 x i8], [12 x i8]* @str.2, i32 0, i32 0))
+; CHECK-NEXT:    ret void
+;
+  %fmt = getelementptr [3 x i8], [3 x i8]* @format_str, i32 0, i32 0
+  %str1 = getelementptr [1 x i8], [1 x i8]* @empty, i32 0, i32 0
+  call void (i8*, ...) @printf(i8* %fmt, i8* %str1, i32 42, double 0x40091EB860000000)
+  %str2 = getelementptr [2 x i8], [2 x i8]* @charstr, i32 0, i32 0
+  call void (i8*, ...) @printf(i8* %fmt, i8* %str2, i32 42, double 0x40091EB860000000)
+  %str3 = getelementptr [13 x i8], [13 x i8]* @hello_world, i32 0, i32 0
+  call void (i8*, ...) @printf(i8* %fmt, i8* %str3, i32 42, double 0x40091EB860000000)
+  ret void
+}
Index: llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
===================================================================
--- llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
+++ llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
@@ -2377,14 +2377,24 @@
   if (FormatStr.size() == 1 || FormatStr == "%%")
     return emitPutChar(B.getInt32(FormatStr[0]), B, TLI);
 
-  // printf("%s", "a") --> putchar('a')
+  // Try to remove call or emit putchar/puts.
   if (FormatStr == "%s" && CI->getNumArgOperands() > 1) {
-    StringRef ChrStr;
-    if (!getConstantStringInfo(CI->getOperand(1), ChrStr))
+    StringRef OperandStr;
+    if (!getConstantStringInfo(CI->getOperand(1), OperandStr))
       return nullptr;
-    if (ChrStr.size() != 1)
-      return nullptr;
-    return emitPutChar(B.getInt32(ChrStr[0]), B, TLI);
+    // printf("%s", "") --> NOP
+    if (OperandStr.empty())
+      return (Value *)CI;
+    // printf("%s", "a") --> putchar('a')
+    if (OperandStr.size() == 1)
+      return emitPutChar(B.getInt32(OperandStr[0]), B, TLI);
+    // printf("%s", str"\n") --> puts(str)
+    if (OperandStr.back() == '\n') {
+      OperandStr = OperandStr.drop_back();
+      Value *GV = B.CreateGlobalString(OperandStr, "str");
+      return emitPutS(GV, B, TLI);
+    }
+    return nullptr;
   }
 
   // printf("foo\n") --> puts("foo")


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