dev:crosscompiler:backend:register_allocator
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| Both sides previous revisionPrevious revisionNext revision | Previous revisionNext revisionBoth sides next revision | ||
| dev:crosscompiler:backend:register_allocator [2018/02/28 14:42] – [Resolving of Phi-Functions] ursgraf | dev:crosscompiler:backend:register_allocator [2018/02/28 14:43] – [Determine Used Parameters] ursgraf | ||
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| Before the phi-functions can be resolved, loops need special treatment. Let's consider the folowing case: | Before the phi-functions can be resolved, loops need special treatment. Let's consider the folowing case: | ||
| [{{ .: | [{{ .: | ||
| - | {{: | ||
| The SSAValue of //a// is used in the loop. The live range of //a// extends to the instruction for //b = 2 * a//. However, this would be wrong, because the register for //a// would be released at this point and might be used otherwise. It must stay reserved until the end of the loop. At the beginning of node 2 a phi-function is created for //a//. This function will be deleted because //a// is set in node 1 and only read in node 2. For all phi-functions in loops (whether deleted or not) the field //last// is set to the last instruction of this loop.\\ | The SSAValue of //a// is used in the loop. The live range of //a// extends to the instruction for //b = 2 * a//. However, this would be wrong, because the register for //a// would be released at this point and might be used otherwise. It must stay reserved until the end of the loop. At the beginning of node 2 a phi-function is created for //a//. This function will be deleted because //a// is set in node 1 and only read in node 2. For all phi-functions in loops (whether deleted or not) the field //last// is set to the last instruction of this loop.\\ | ||
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| ===== Determine Used Parameters ===== | ===== Determine Used Parameters ===== | ||
| - | Parameters are passed in volatile registers. Some of them have to be copied to nonvolatile registers. Some parameters might not be used at all in a method. This can be determined in the exit set of the last node. If a value is null in that set the parameter with this index was never loaded and hence no register must be reserved. The following example demonstrates parameter usage. | + | Parameters are passed in volatile registers. Some of them have to be copied to nonvolatile registers. Some parameters might not be used at all in a method. This can be determined in the exit set of the last node. If a value is null in that set the parameter with this index was never loaded and hence no register must be reserved. The following example demonstrates parameter usage on a ppc platform. |
| <code java> | <code java> | ||
| float m2(long a, float b, double c, byte[] d, short e, int f, int g) { | float m2(long a, float b, double c, byte[] d, short e, int f, int g) { | ||
dev/crosscompiler/backend/register_allocator.txt · Last modified: 2019/08/29 16:53 by ursgraf
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