cmd/compile: optimize away redundant assignments #597
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ints behave a little bit better. For example, if I do: var a int a = 7 a = 6 ... With 6g I get: 0000 (test.go:11) TEXT main+0(SB),$72-0 0001 (test.go:6) MOVL $0,AX 0002 (test.go:9) MOVL $6,a+-28(SP) ... So the first MOV isn't optimized away, but the one for a = 7 is. It wouldn't be for a float. It also seems strange that the MOVs are using different destinations, but that's probably a separate issue. |
I have a fix pending for the integer case, which can be done by the optimizer. The floating point case is more difficult: it really needs to be done during code generation. That may happen with some analysis that is planned, but it's not trivial. It may be ready for Go 1.1 but may not. Labels changed: added go1.1maybe, removed go1.1. |
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Fixed by the new SSA backend. |
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I have the following program: func main() { var a float a = 6.7 ... } Here is the assembly generated with 6g: 0000 (test.go:12) TEXT main+0(SB),$72-0 0001 (test.go:6) MOVSS $(0.00000000000000000e+00),X0 0002 (test.go:8) MOVSS $(6.70000000000000000e+00),X0 ... I would expect the first MOVSS to be optimized away. Subsequent assignments generate more instructions still. 5g and 8g also generate similar instructions. Which revision are you using? (hg identify) c20b85c872e5+ tipThe text was updated successfully, but these errors were encountered: