[SLC] Add an alignment to printf->puts global string

[dmgreen]

Summary

Previously the alignment on the newly created puts string was not set,
meaning that DataLayout::getPreferredAlignment was free to overalign
it to 16 bytes. This causes unnecessary code bloat.

[efriedma]

CreateGlobalString itself should probably set the alignment on the global.

[dmgreen]

Moved to CreateGlobalString

[efriedma]

LGTM

[davide]

lgtm

lib/Transforms/Utils/SimplifyLibCalls.cpp

Value *LibCallSimplifier::optimizePrintFString(CallInst *CI, IRBuilder<> &B) {
   }
 
   // printf("foo\n") --> puts("foo")
   if (FormatStr[FormatStr.size() - 1] == '\n' &&
       FormatStr.find('%') == StringRef::npos) { // No format characters.
     // Create a string literal with no \n on it.  We expect the constant merge
     // pass to be run after this pass, to merge duplicate strings.
     FormatStr = FormatStr.drop_back();
-    Value *GV = B.CreateGlobalString(FormatStr, "str");
+    GlobalVariable *GV = B.CreateGlobalString(FormatStr, "str");
+    GV->setAlignment(1); // Prevent the string from being over-aligned
     return emitPutS(GV, B, TLI);
   }
 
   // Optimize specific format strings.
   // printf("%c", chr) --> putchar(chr)
   if (FormatStr == "%c" && CI->getNumArgOperands() > 1 &&
       CI->getArgOperand(1)->getType()->isIntegerTy())
     return emitPutChar(CI->getArgOperand(1), B, TLI);

test/Transforms/InstCombine/printf-1.ll

 ; Test that the printf library call simplifier works correctly.
 ;
 ; RUN: opt < %s -instcombine -S | FileCheck %s
 ; RUN: opt < %s -mtriple xcore-xmos-elf -instcombine -S | FileCheck %s -check-prefix=CHECK-IPRINTF
 
 target datalayout = "e-p:32:32:32-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:32:64-f32:32:32-f64:32:64-v64:64:64-v128:128:128-a0:0:64-f80:128:128"
 
 @hello_world = constant [13 x i8] c"hello world\0A\00"
 @h = constant [2 x i8] c"h\00"
 @h2 = constant [3 x i8] c"%%\00"
 @percent = constant [2 x i8] c"%\00"
 @percent_c = constant [3 x i8] c"%c\00"
 @percent_d = constant [3 x i8] c"%d\00"
 @percent_f = constant [3 x i8] c"%f\00"
 @percent_s = constant [4 x i8] c"%s\0A\00"
 @empty = constant [1 x i8] c"\00"
-; CHECK: [[$STR:@[a-z0-9]+]] = private unnamed_addr constant [12 x i8] c"hello world\00"
+; CHECK: [[$STR:@[a-z0-9]+]] = private unnamed_addr constant [12 x i8] c"hello world\00", align 1
 
 declare i32 @printf(i8*, ...)
 
 ; Check printf("") -> noop.
 
 define void @test_simplify1() {
 ; CHECK-LABEL: @test_simplify1(
   %fmt = getelementptr [1 x i8], [1 x i8]* @empty, i32 0, i32 0