instcombine: Migrate ffs* optimizations

This patch migrates the ffs* optimizations from the simplify-libcalls
pass into the instcombine library call simplifier.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@168571 91177308-0d34-0410-b5e6-96231b3b80d8

test/Transforms/SimplifyLibCalls/FFS.ll

@@ -1,45 +0,0 @@
-; Test that FFSOpt works correctly
-; RUN: opt < %s -simplify-libcalls -S | FileCheck %s
-
-; CHECK-NOT: call{{.*}}@ffs
-
-@non_const = external global i32		; <i32*> [#uses=1]
-
-declare i32 @ffs(i32)
-
-declare i32 @ffsl(i32)
-
-declare i32 @ffsll(i64)
-
-define i32 @main() {
-	%arg = load i32* @non_const		; <i32> [#uses=1]
-	%val0 = call i32 @ffs( i32 %arg )		; <i32> [#uses=1]
-	%val1 = call i32 @ffs( i32 1 )		; <i32> [#uses=1]
-	%val2 = call i32 @ffs( i32 2048 )		; <i32> [#uses=1]
-	%val3 = call i32 @ffsl( i32 65536 )		; <i32> [#uses=1]
-	%val4 = call i32 @ffsll( i64 1024 )		; <i32> [#uses=1]
-	%val5 = call i32 @ffsll( i64 17179869184 )		; <i32> [#uses=1]
-	%val6 = call i32 @ffsll( i64 1152921504606846976 )		; <i32> [#uses=1]
-	%rslt1 = add i32 %val1, %val2		; <i32> [#uses=1]
-	%rslt2 = add i32 %val3, %val4		; <i32> [#uses=1]
-	%rslt3 = add i32 %val5, %val6		; <i32> [#uses=1]
-	%rslt4 = add i32 %rslt1, %rslt2		; <i32> [#uses=1]
-	%rslt5 = add i32 %rslt4, %rslt3		; <i32> [#uses=2]
-	%rslt6 = add i32 %rslt5, %val0		; <i32> [#uses=0]
-	ret i32 %rslt5
-}
-
-
-; PR4206
-define i32 @a(i64) nounwind {
-        %2 = call i32 @ffsll(i64 %0)            ; <i32> [#uses=1]
-        ret i32 %2
-}
-
-; PR13028
-define i32 @b() nounwind {
-  %ffs = call i32 @ffsll(i64 0)
-  ret i32 %ffs
-; CHECK: @b
-; CHECK-NEXT: ret i32 0
-}