cmd/compile: removing log2uint32 function

Just using isUnsignedPowerOfTwo and log32u is enough.

Change-Id: I93d49ab71c6245d05f6507adbcb9ef2a696e75d6
Reviewed-on: https://go-review.googlesource.com/c/go/+/691476
Reviewed-by: Keith Randall <[email protected]>
Reviewed-by: Keith Randall <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>
Auto-Submit: Cuong Manh Le <[email protected]>
Reviewed-by: David Chase <[email protected]>

Author: cuonglm

src/cmd/compile/internal/ssa/_gen/MIPS.rules

@@ -607,13 +607,13 @@
 (Select0 (MULTU (MOVWconst [1])  _ )) => (MOVWconst [0])
 (Select1 (MULTU (MOVWconst [-1]) x )) => (NEG <x.Type> x)
 (Select0 (MULTU (MOVWconst [-1]) x )) => (CMOVZ (ADDconst <x.Type> [-1] x) (MOVWconst [0]) x)
-(Select1 (MULTU (MOVWconst [c])  x )) && isPowerOfTwo(int64(uint32(c))) => (SLLconst [int32(log2uint32(int64(c)))] x)
-(Select0 (MULTU (MOVWconst [c])  x )) && isPowerOfTwo(int64(uint32(c))) => (SRLconst [int32(32-log2uint32(int64(c)))] x)
+(Select1 (MULTU (MOVWconst [c])  x )) && isUnsignedPowerOfTwo(uint32(c)) => (SLLconst [int32(log32u(uint32(c)))] x)
+(Select0 (MULTU (MOVWconst [c])  x )) && isUnsignedPowerOfTwo(uint32(c)) => (SRLconst [int32(32-log32u(uint32(c)))] x)
 
 (MUL (MOVWconst [0])  _ ) => (MOVWconst [0])
 (MUL (MOVWconst [1])  x ) => x
 (MUL (MOVWconst [-1]) x ) => (NEG x)
-(MUL (MOVWconst [c]) x ) && isPowerOfTwo(int64(uint32(c))) => (SLLconst [int32(log2uint32(int64(c)))] x)
+(MUL (MOVWconst [c]) x ) && isUnsignedPowerOfTwo(uint32(c)) => (SLLconst [int32(log32u(uint32(c)))] x)
 
 // generic simplifications
 (ADD x (NEG y)) => (SUB x y)

src/cmd/compile/internal/ssa/rewrite.go

@@ -492,12 +492,6 @@ func log16u(n uint16) int64 { return int64(bits.Len16(n)) - 1 }
 func log32u(n uint32) int64 { return int64(bits.Len32(n)) - 1 }
 func log64u(n uint64) int64 { return int64(bits.Len64(n)) - 1 }
 
-// log2uint32 returns logarithm in base 2 of uint32(n), with log2(0) = -1.
-// Rounds down.
-func log2uint32(n int64) int64 {
-	return int64(bits.Len32(uint32(n))) - 1
-}
-
 // isPowerOfTwoX functions report whether n is a power of 2.
 func isPowerOfTwo[T int8 | int16 | int32 | int64](n T) bool {
 	return n > 0 && n&(n-1) == 0